Sunday, December 9, 2012

My experience

Thanks to this student blog, over the semester, I have deepened my knowledge of some very useful astronomy concepts.  I have learned more about binary systems, black holes, star formation, exoplanets, and many other extremely interesting astronomy concepts. 

Astronomy is my major and it is a very important part of my life so doing something i love and getting to express some of my thoughts about it to this big internet community has been a blessing.  I loved the fact that I got so many views and I even got comments and or questions on some of my blog posts.  I have to say that I liked the questions the most because they were really good questions. 

I want to thank everyone for ready this blog and I hope you all will continue to read the blog in the future!


Tuesday, December 4, 2012

Colloquium November 29

On November 29, 2012 the University of Michigan welcomed Andy Fabian to speak on Black holes and their environments.

Andy Fabian is a professor at the University of Cambridge. He has received many awards through out his career and he has taught around the world.

During his lecture Fabian focused primarily on the way we view black holes. He talked about how the amount of radiation (energy from matter around the black hole) depends on what surrounds the black hole.  He gave details about how we view the spectra of the released energy. He said that the radiation that is sent out by black holes is often in the X-ray band because it has such high energy. 

Fabian talked about how the energy of a black hole varies if it has a spinning accretion disk or a non spinning accretion disk.  He said that spinning accretion disks release 5 times more energy (radiation) than non spinning disks release.  He also said that some black hole shoot jets and these jets can go out as far as 5 Mpcs.

Monday, December 3, 2012

Black hole's affected by surrounding matter

Many black holes are affected by matter that is found around them. These objects that affect black       holes include orbiting stars, gas, planetary objects, comets, asteroids,  and many other celestial object.

When Black holes are affected astronomers can view the effects through X-ray emissions from the luminous black holes.  Astronomers, through X-ray emissions, can see the black hole's strong gravitational affects, its gravity redshifts, its gravitational light bending, its delays, and its dragging of inertial frames in the Kerr metric. 

The accretion disks that surround black holes include lots of dust that affect the energy outputs of the black holes.  These disks can create soft X-ray emission or hard X-ray emission.  These accretion disks can surround both spinning and non spinning black holes.  However, spinning black holes produce 5 times as much power as non spinning black holes.

End of Term Evaluation

If you've been reading this blog this term, we'd really appreciate it if you could take a minute or two to let us know what you thought.
It really is quick!

Tuesday, November 27, 2012

Colluqium November 15

On November 15, 2012 the University of Michigan welcomed Dennis Bodewits to speak on comets and asteroids.

Dennis Bodewits is an assistant research scientist in the Astronomy Department at the University of Maryland.  "His research emphasizes comets and asteroids, and he is a member of the EPOXI/Deep Impact and Stardust-Next science teams. His observational studies encompass X-ray, UV and visible regions, and makes use of mostly space-born telescopes, such as Swift, Chandra, and XMM-Newton".(

In his speech Bodewits focused on the roles comets and asteroids played in the creation of water on Earth.  He had videos and many photos of artistic interpretations of water formation of Earth. Bodewits also gave detailed explanations of the compositions of asteroids and comets.

For more information on comets here is a link: For more information on asteroids here is a link: For more information on water formation on Earth here is a link:

Saturday, November 24, 2012

The Water of Earth. The Contribution of Asteroids, Comets, and Meteors

Earth is a fascinating and amazing planet to study because it has surface water. Surface water is an extremely valuable resource. It is arguably the most valuable resource on Earth because it is essential to all living organisms and it formed over a large amount of time. Water formed on Earth through a process that lasted millions of years. 

The process that allowed water to form on Earth included; asteroids, comets, and meteors. Astronomers have many theories about this process. Some astronomers have different beliefs about the ratio of comets, meteors, and asteroids that were involved in the formation of water on Earth. All of the different theories that involve the different ratios and time scales can all be justified because no one really knows how water formed on the surface of the Earth. It is impossible to know because humans had not even been created when water formed on Earth. However, astronomers know that asteroids, meteors, and comets played a role in water formation on the surface of earth because the water had to have come from some outside source. 

Asteroids, comets, and meteors are very important celestial bodies that have been found in our solar system. Most importantly asteroids, comets, and meteors, contributed to water formation on the surface of the Earth. These celestial bodies, any natural body outside of the solar system, have been studied for many years and they are all very different from one another. Their differences make them very interesting. 

Asteroids are airless objects, most commonly found in the asteroid belt. The asteroid belt is located Mars and Jupiter. For more information on asteroids here is a link

Comets are icy objects, most commonly found in the Oort cloud. The Oort cloud is a spherical cloud located 50,000 AU from the Sun. For more information on comets here is a link

Meteors are dust to bolder sized particles of debris that are found in the solar system. 
Meteorites that astronomers have studied on Earth have hydrogen isotope ratios that help explain how elements like hydrogen and nitrogen got on the Earth. 

The biggest question astronomers are trying to answer is how volatiles like hydrogen, nitrogen, and carbon first arrived on Earth. Astronomers mostly believe that these elements arrived on Earth through collisions with comets and asteroids. One of the most accepted theories on how water formed on Earth suggests that during the creation of the solar system Jupiter and Saturn's orbits were disturbed and that caused comets in the outer solar system to move inward and later make their way towards Earth. These comets collided with Earth and left ice and other elements behind. Later when an asteroid collided with the Earth, the ice was melted and liquid water was then formed on the surface of the Earth. This process, according to astronomers, happened many times and it took millions of years.

Friday, November 23, 2012


Comets are known as “dirty snowballs,” because they consist of a mixture of ices (both of water and frozen gases), carbon dioxide, ammonia, methane, and dust. The core of a comet is solid and it consists of ice and dust.

Comets also have two tails. The first tail is an ion tail. The ion tail is blue because it consists of ionized CO+ and it scatters blue light. The second tail is the dust tail. The dust tail is green and consists of the dust that is pushed off of the comet and reflects radiation from other sources. The tails of a comet can reach 160 million kilometer long. 

The average comet has a mass of 10^14 kg, a diameter of 20 km, a density of 0.6 g/cm^3, and an albedo of .05.

Comets are mostly located in the Oort cloud, except for the occasional comets that streaks through the inner solar system. The Oort cloud holds millions and millions of comets and the Oort cloud is found much farther out than the orbit of Pluto. It is generally believed that we got our water when comets collided with the Earth.

Thursday, November 22, 2012


Asteroids are marvelous celestial objects, not only because they played a huge role in water formation on Earth through various collisions with Earth's surface, but because they are so complex. Asteroids are irregularly shaped, rocky objects that usually are considered small objects or minor planets. They are rocky fragments that were left over from 4.6 billion years ago when the solar system formed. 

 The average asteroid is very complex because it has a diameter of 20 km, a density of 0.3 g/cm^3, and an albedo of less than .05. They also have an average surface temperature of 100 degrees Fahrenheit. 

 Asteroids are also very interesting because they fall into three different categories based on their compositions; C-type (carbonaceous) asteroids, S-type (sillicaceous) asteroids, and M-type (metallic) asteroids. C-type asteroids are greyish and are the most common asteroids. They make up 75 percent of all known asteroids in the solar system. S-type asteroids are reddish and greenish in color and they make up 17 percent of all known asteroids. M-type asteroids are red in color, consist of mostly nickle, and are located mostly in the middle of the asteroid belt. 

 Asteroids orbit the Sun in elliptical orbits in the asteroid belt that is located between Mars and Jupiter. The asteroid belt is made up of many different sized asteroids. The asteroid belt holds more than a million asteroids, of which 200 are larger than 60 km in diameter and 750,000 are larger than 1 kilometer in diameter. Half of the mass that is found in the asteroid belt comes from the four largest asteroids. The four largest asteroids are Ceres, Vesta, Pallas, and Hygiea. 

 The total mass of all the asteroids in the solar system is less than the mass of the Moon, but asteroids are still very dangerous. Many asteroids collided with the Earth in the past. The asteroids that collided with the Earth, depending on their sizes, caused great amounts of damage. Therefore many astronomers study the orbital paths of asteroids and believe that these earlier collisions, together with earlier comet collisions, contributed to water formation on Earth's surface.

Monday, November 12, 2012

Colloquia November 8

On November 8, 2012 the University of Michigan welcomed back a former graduate student Zhaohuan Zhu. 

Zhaohuan Zhu was a graduate student at the University of Michigan some years ago. He now students at Princeton.

Zhu focused of the fluid dynamics of planetary system formations. He described why he believed it was better to used 3D over 2D simulations. He said it was better because we could see more data about the way a planetary system works.

He went into great detail about how planets form. He talked about using radio velocities techniques (measuring the wobble of the planet) and imaging (viewing the planet head on).

Zhu also showed a very interesting video about the Almer telescope and its array formation. It is composed of many radio telescopes to give astronomers a deeper clearer view of the universe.With the Almer telescope astronomers will be able to view deeper into space as far back as many radio waves, and since they are in an array they are not limited by the viewing power of the telescope itself. They are all put together as one so essentially the viewing power is only limited by the amount of telescopes in the array.

Planetary System Formations

Planetary System Formations

To understand how planetary systems form I will focus on the Solar system because it is the most widely studied system. Astronomers believe the nebular hypothesis when it comes to the solar system. They believe that the solar system formed from the collapse (gravitationally) of a portion of a very big molecular cloud. The formation of the Solar system occurred about 4.55 billion years ago

The molecular cloud was most likely about 20 pc and the part that actually collapsed to form the solar system was about 1 pc or 20,000 AU in size. 

Here is a picture of a molecular cloud:

The 1 pc region included a mass of a little bit more than the Sun (around 1.98*10^30 kilograms). Hints: the sun is the most massive object in the Solar system. This region was composed of primarily Hydrogen and Helium with very tiny amounts of lithium.

The molecular cloud at a certain point began to spin very fast because of angular momentum. The atoms inside cloud began to collide and they converted their kinetic energy into heat. As it continued to collapse the center of it was much hotter than is surrounding disk. After about 100,000 years the forces of gas pressure and gravity competing led to the formation of a protostar . After 50 million years the protostar became hot enough to fuel itself through nuclear fusion and the protostar became what is known as the Sun.

The planets in the solar system formed from the disc shaped cloud containing dust and gas that the sun left after its formation. Astronomers believe that the planets (like the earth) began as grains of dust and accumulated matter over years until they became planets. This process is very inefficient according to Astronomers when compared to star formation. While the gas giants in the solar system formed much farther out.

Sunday, November 11, 2012

What is a Planetary System?

Astronomers have studied the Solar system for many years and because of this they know that planetary systems take 1 to 10 million years to form.

Here is a general picture of what a planetary system could looks like:

A planetary system is a collection of gravitationally bound celestial objects that orbit around a star or a system of stars.  These systems vary in sizes and vary in the amount of planets they contain.  Astronomers have frequently discovered single planetary systems using radial velocity method calculations.

Planetary systems usually describe systems with one or two planets and a star, but these systems can contain multiple stars, multiple planets, satellites, dwarf planets, asteroids, meteoroids, and comets.

Tuesday, November 6, 2012

Astronomy Colloquia 11/1

On November 1, 2012 the Astronomy department at the University of Michigan held a Colloquia. Jason Wright, an assistant professor of astronomy and astrophysics at Pennsylvania State University, was the main speaker.

Wright is a member of the Center of Exoplanets for Habitable Worlds and the Penn State Astrobiology Research Center (part of the NASA Astrobiology Institute). He study stars, their atmospheres, their activity and their planets.

During his speech he focused on the detection and the discovery of exoplanets.  Exoplanets are planets that are discovered outside of the solar system. for more info on exoplanets go here: His speech was very interesting because it described the indirect (for more information:  and direct (for more information: methods of detecting exoplanets in detail.  He also described how hard it is to detect a habitable planet and the key components that define an exoplanet as habitable or non habitable. 

Monday, November 5, 2012

Direct Exoplanet Detection

There are two methods used to directly detect exoplanets.

The first direct method used is referred to as imaging. Planets are light sources, although sometimes very faint light sources. To discover exoplanets using this method observers can see light produced by an exoplanet. Using this method is extremely difficult because older or middle aged exoplanets produce very little light, especially if they are small. This method has usually only worked when observing hot young exoplanets. The light produced by the exoplanets' companion star can literally out shine the light produced by the exoplanet and the exoplanet can go undetected. 


The second direct method is infrared interferometry. Traditionally telescope's viewing power is limited by the diameter of the telescope's mirror or lens, but combining telescopes in an array can greatly boost a telescopes viewing power. Array telescope in space can then use infrared interferometry to detect exoplanets and their companion stars. This method is the newest method of detecting exoplanets but it seems to be the most promising because array telescopes could potentially easily detect exoplanets that take years to detect using other methods.

Indirect Exoplanet detection

 There are four indirect methods used to detect exoplanets.

The first method indirect is the radial velocity method. It is the most common method used to discover exoplanets. The reflex motion of a star due to the orbiting planet is measures as a change in a stars radial velocity. The radial reflex of the star is compared to the exoplanets orbit, using the measurements of Doppler shifts. These comparisons are used to calculate the mass of the exoplanet, its orbits shape, and its orbital distance. The exoplanets discovered using this method tend to be very low mass planets. 

 The second indirect method is the astrometry method. This method measures a star's position and how it changes over time so is mostly used to discover exoplanets that have very long periods.  After that you can use the acquired information to determine the actual mass of the exoplanet because you can determine the orbital plane of the exoplanet. The best place to use astrometry is in space but you can use this method from the surface of earth. The exoplanets discovered using this method tend to be very far from the solar system. 

The third indirect method is the transit method. A transit is an event that occurs when a celestial object moves in-front of another celestial object. When the celestial body moves infront of the other larger celestial body it hides a small portion of it. Observers can see this occurrence at particular orbital points. This method reveals exoplanets when they transit their larger companion stars. Observers see a drop in the visual brightness of the companion star. The exoplanets orbit has to be perfectly aligned with the observers viewing point or the observer could easily miss the exoplanet. Also there is a very high amount of false exoplanet detections when using the transit method because dust, gas, and even planetary debris can easily cause a star to appear dimmer. 

The fourth indirect method is gravitational lensing. Gravitational lensing occurs when the presence of matter effects the path of a light ray. The light ray, from the observers view can appear to be curved or highly unusual. The gravity field of a star can behave like a lens and it can magnify the light of a background star. The star, the background star, and the Earth all move relative to each other. If the lensing star has a companion exoplanet, then the exoplanet's gravitational field can be detected through its contribution to lensing effect. This effect only occurs when the stars are almost perfectly aligned. The lensing events are very short and they can never be repeated so it is very difficult to detect exoplanets using this method.

Sunday, November 4, 2012


An exoplanet is a planet that is found outside of the solar system.  Exoplanets are also referred to as extrasolar planets.

Astronomers use many different techniques to locate these planets. Astronomers have discovered 843 exoplanets, 663 are in single planetary systems and there are 126 exoplanets in multiple planetary systems. Astronomers have predicted that there are above a billion exoplanets in the Milky Way galaxy.

Below is an example of an exoplanet orbiting in a binary star system:

To discover exoplanets astronomers use three techniques. The first technique involves using precise radial velocities, and this technique is the most commonly used. The second technique is the transit method, and the third is imaging.  Imaging is the hardest method of discovering exoplanets used be astronomers.

Here is a picture of some of the discovered exoplanets compared to their companion stars:

Tuesday, October 30, 2012

Colloquia October 25 2012

On October 25, 2012 the astronomy department welcomed a guest from  Michigan State University.

Jay Strader is a MSU assistant professor in the fields of physics and astronomy.  He also completed

research at Santa Cruz.

During the Colloquia he focused his lecture on globular clusters and binaries. 

Globular clusters are very old, because of this all of the higher mass stars, that were originally found in the cluster, are all in their final stage of life.  In Globular clusters black holes behave irregularly. They do not behave the way we see them behave in less dense, more massive, galaxies. In globular clusters astronomers have discovered many black hole binaries. In these binaries two black holes orbit around each other. There have been between 100 and 1000 black holes discovered in globular clusters and many of them are in binary systems. It is estimated that there were at one time in history many more black holes but those black holes were ejected from the globular clusters. Astronomers believe that black holes are ejected when they try to join a already gravitationally bound two black hole binary. The third black hole is considered a “third wheel” and is sent flying off into space after the two black hole binary steals an extremely high amount of its energy. This process produces an immense amount of X-ray emission and it produces radio emission from the jets of matter that stream out from the top and bottom of the black holes.

Monday, October 29, 2012

Black holes in Gobular Clusters

Globular clusters are old star clusters.  For more information:

Globular clusters are very old, upwards of 12 billion years old. Since they are so old all of the higher mass stars, that were originally found in the cluster, are all dead.  When I say dead I mean they have already passed through all the stages of a normal star ( and now are black holes. Black holes are high density objects that emit no light. For more information:

There are usually 100 to 1000 black holes in globular cluster.  Since globular clusters have very dense environments astronomers have discovered many black hole binary systems.  These binaries can produce extremely high amounts of X-ray emission because the two black holes magnetic fields interact.

Wednesday, October 24, 2012

Globular Clusters

In our galaxy we can find many globular clusters. There are around 158 known globular clusters in our galaxy. These clusters are most often found in the galactic halo, but they do orbit the center of the Milky Way.

A globular cluster contains around 1 million stars and they are about 15 parsecs in diameter.  This means that the stars in the clusters are very close together.

Globular clusters actually help astronomers look back in time because they are all around 12 billion years old. Since they are 12 billion years old the stars in the globular clusters are all very old, red, and have low masses.  This is why globular cluster sometimes appear red in images.  

Globular clusters are very tightly bound by gravity.  If you look at images of globular clusters you can observe that their centers are very bright and stars have more distance between them the farther they are located from the center.

Friday, October 19, 2012

October 18 Astronomy Colloquia

On October 18, the astronomy department welcomed back Matthew Walker, a former graduate student at U of M.  He came back and gave a talk on dwarf galaxies ( and how they can be used to determine the composition of dark matter (

He went into great detail about how dark matter effects dwarf galaxies.  According to his observations dwarf galaxies are composed of nearly 99% dark matter, while the other 1% is real matter that can produce radiation.  Stars are included in the 1% of real matter in the dwarf galaxies.

Walker also told us that last summer radiation was detected from the center of the Milky Way and that, that radiation is hypothesized to be dark matter. On June 15, 2012 Douglas P. Finkbeiner observed strong evidence for gamma-ray emission from the center of the Milky Way.

One of the most interesting things that Walker told us was that dark matter was probably neither cold nor hot.  Based on his calculations dark matter can not be cold and based on the calculations at the big bang it was very unlikely that dark matter is hot.  That leaves us with warm dark matter, but the problem is how do we determine what it is comprised of.  This question will remain a mystery for years to come, but hopefully someone figures it out soon because I really want to know what dark matter is!

Dwarf Galaxies

There are 3 main types of galaxies in our universe; elliptical, spiral, and irregular.  Sometime galaxies form with considerably less stars than usually. Astronomers call these galaxies dwarf galaxies.  They can still fall into the 3 categories but they are much smaller.

An elliptical galaxy is a galaxy that has an ellipsoidal shape.  Most elliptical galaxies are composed of low-mass older stars. Here is a picture of an elliptical galaxy:

A spiral galaxy is a galaxy that has spiral arms, a disk, and a bulge.  The spiral arms contain young stars, while the disk and bulge contain the older stars in the galaxy. An example of a spiral galaxy is the Milky Way and here is a photo:

 An irregular galaxy is just a galaxy that cannot be classified as either spiral or elliptical. Here is a photo of one:

Dark Matter

The Universe is composed of 4% baryonic matter (real matter; protons, neutrons, electrons, etc), 73% dark energy, and 23% dark matter (1). Dark matter is estimated to make up 85% of the matter in the universe and the other 15% is made up of ordinary matter. Dark matter is referred to as dark because we cannot see it. Astronomers believe that there is hot, warm, and or cold dark matter. Dark matter is thought to be composed of non-baryonic and baryonic matter.

Astronomers hypothesize that hot dark matter is comprised of particles that have non-zero masses (2). The most popular hot dark matter particle is the neutrino. In 1930, Wolfgang Pauli first proposed the theory of neutrinos and in 1933, Enrico Fermi created the term Neutrino. Neutrinos are particles that are similar to electrons but they do not hold a negative charge like electrons, they hold no charge at all (3). Neutrinos can pass through great distances of matter and not be affected at all.   Since neutrinos are neutral, electromagnetic forces do not affect them (2). The only thing that can affect a neutrino is a weak sub-atomic force. There are three types of neutrinos; there is the electron neutrino, the muon, and the tau (3). Neutrinos also have what is called high-integer half spin.

Cold dark matter is theorized to be made up of WIMP (Weakly Interacting Massive Particles) and MACHOs (Massive Astrophysical Compact Halo Objects) (1). WIMPs are thought to be composed of massive Dirac neutrinos (4). The neutrinos that theoretically make up WIMPS are heavy fourth generation neutrinos. MACHOs are composed of normal baryonic matter that do not emit radiation. MACHOs could be black holes, brown dwarfs, neutron stars, planets, white dwarfs, and or extremely faint red dwarfs.

Although Dark matter cannot be seen it has been detected in many other ways. The first person to discover the presence of dark matter was Jan Oort. Oort, was a Dutch astronomer who studied radio astronomy. Oort discovered that the mass of galactic plane had to be more than what could be seen. When he discovered this he was studying stellar motions in surrounding of the local galactic area.
Dark matter can be detected when observing galactic rotational curves, the gravitational lensing of galaxy clusters, and by the velocity dispersions in galaxies (5). If we look at the Milky Way the way the stars in the arms move and the way the objects rotate around the Milky Way does not make since until we introduce more matter into the equation. If we only look at the visible matter in the Milky Way, the behavior of the objects inside the Milky Way do not make since. Gravitational lensing is the process by which space-time is curved by matter (5). The matter curves the space-time so light is then deflected. Gravitational lensing pertains to dark matter because non-visible matter has been confirmed to defect light (5). Dark matter also explains the high rotational speeds of galaxies (6). If these galaxies did not have the hidden dark matter they would be torn apart (6). 

  1. National Aeronautics and Space Administration. Dark Energy, Dark matter.
  2. The neutrino and its friends. Dave Casper.
  3. Gravitational lensing. Jcohn. Berkley. Dec 13, 2010.
  4. Gravity Lens reveals dark matter. Bob Swarup. Aug 25, 2006.

Monday, October 15, 2012

Doug Lin

Doug Lin was a guest of the University of Michigan Astronomy department last week, and on October 11 he gave a talk on planetary system formations. 

Doug Lin is a professor of Astronomy and Astrophysics at the University of California in Santa Cruz. For more info check here

Lin's talk focused primarily on the origin, evolution, and destiny of close-in Super Earths. Super Earths are in simpler terms "Earth-like" planets. He went into detail about his work. He explained that new data that has been obtained from Kepler transit surveys and systematic radial velocity surveys, led to the discovery of 700 planets and 3000 other planetary candidates.  These planets have diverse structures and they are found orbiting stars. 

Lin plans on using his data to find the origin, destiny, and evolution of these planets. Keep a look out for Lin's future discoveries because we will need a new planet in 4.5 billion years.

Earth-Like Planets

Over the past 2 or 3 years there have been several discoveries of "Earth-like" planets. I use quotations over "Earth-like" because we have no way of actually knowing if these planets could sustain human life.

For a planet to be categorized as "Earth-like," it has to orbit a star.  The star must have a certain mass and it must produce a certain amount of radiation (heat). The star must not be close enough to toast the planet hint hint: Mercury.  This planet must fall into a distance range that gives the planet a balance between hot and cold temperatures. The planet usually is somewhere around Venus's orbit  but not much further out than were Mar's orbit is (in distance terms of our solar system). "Earth-like" planets can be much bigger than earth or much smaller (probably not as small as Pluto).

Astronomers have discovered many planets that fall into the category of "Earth-like," but understand that these planets are not necessarily like the Earth.  These planets "could" be able to support life, but on the other hand they could be dangerous. Weather on the planets could be very severe; storms, hurricanes, tornadoes etc. could all be devastating.  Also the planets could be dangerous as in Mars (very cold, bad atmosphere) or Venus (crushing atmosphere, temperatures that kill.)

As far as I am concerned the human population better find a planet to migrate to soon or we will all be toast.  If you plan on living on Earth for another 4.5 billion years, you better prepare yourself for a big move. Make sure to pack light as there will be a lot of people moving at the same time. Oh yeah, take pictures and post them to facebook. Don't forget to tag me in the pictures! :)

Tuesday, October 9, 2012

October 4, 2012. Michael Eracleous

On October 4, 2012, the University of Michigan invited Michael Eracleous to give a speech on black hole binary systems and mergers.

Eracleous, pictured below, is a memeber of the Penn state astronomy and astrophysics department.

Eracleous's speech was very detailed about black hole mergers. He focused on how black holes can merge under many different circumstances specifically in black hole binaries. Eracleous also discussed active galactic nuclei. Here is a little background information about AGN ( Active Galactic Nuclei).

Black holes often are gravitationally attracted to each other. This is a proven fact because there are black holes that exceed billions of solar masses. When these black holes initially formed their masses were significantly smaller, so the only way they could have reached these high masses is through black hole mergers.

Astronomers also can estimate the time it takes black holes to merge. In about 4.5 billion years the Andromeda galaxy and the Milky Way galaxy will begin to merge. It will take about 12 billion years for the merger to complete. During the 12 billion years, the black holes at the center of the Milky Way and the center of Andromeda will “seek out” and find each other. Once the merger is complete there will be one big elliptical galaxy and one supermassive black hole at the center of the galaxy, but before the merger is complete these black holes will orbit each other in a binary “like” system. 

In a black hole binary system the two black holes circle each other and are gravitationally bound to each other. Eventually they get so close to each other that they fall into each other. The magnetic fields of the black holes are amplified and matter is evaluated. Then a funnel structure forms and the black holes become one single entity.  After black holes merge there is an accretion disk left behind and material from the accretion disk continuously falls into the black hole until there is no more material in the accretion disk.

Here is a video of this process:

Active Galactic Nuclei

-->Active galactic nuclei are cores of galaxies that produce more radiation than the rest of the galaxy.

 They produce so much radiation that they are studied at all wavelengths of the electromagnetic spectrum. Astronomers typically study them at all energies because they change their behavior constantly. Gamma-ray and X-ray are the most studied bands when it comes to active galactic nuclei because high-energy active galactic nuclei emit most of their power at high energies. The study of X-ray emission is very important because X-ray emission can provide scientists with information about the physical processes occurring in the active galactic nuclei. Gamma-ray emission is important because it gives astronomers information on material that ejects from active galactic nuclei.




Blazars, quasars, and Seyferts are some of the different types of active galactic nuclei. Many astronomers believe that although these active galactic nuclei look different to us, they are actually all the same when viewed in different directions. The most studied type of active galactic nuclei are quasars. Quasars are extremely far away from us, some have been seen as far as 12 billion light-years away. Blazars appear to be extremely bright in the radio band of the electromagnetic spectrum. Seyfrets are the closest active galactic nuclei to our galaxy.

Saturday, September 29, 2012

Black holes, Neutron Stars, and White Dwarfs

The universe is an amazingly entity that scientists have studied for hundreds of years.  Much about our universe has been thoroughly explained but yet there is still so much more that has to be explained.  Stars are arguably the most researched objects in our entire Universe.  Since the dawn of time stars have been visible to the people on earth. Stars are so very interesting to people because they are extremely complex. From the beginning to the end of a stars life cycle there is so much to observe and so much to document.  Stars all begin life the same way but the end of the life cycle of a star is the interesting part. Depending on many different variables a star can end up as a white dwarf, neutron star, or a black hole.  The biggest deciding factor on how a star will end its life, according to many astronomers, is its mass. The Sun and any star with a mass that is around the same as our Sun’s mass will end its life as a white dwarf.  If a star after its final stages of life reaches a mass of over 1.4 solar masses it will become a neutron star. Black holes are produced at the end of a very massive star’s life cycle.  

Above is just a general image of a white dwarf and below is a white dwarf in a binary system that is gaining mass (accretion) from a red giant.

White dwarfs are the most common final stage in the life cycle of most stars in the universe.  There are many more stars in the universe with lower masses (similar to that of our sun’s) then there are massive stars so there are a lot more white dwarfs than neutron stars or black holes (3). A white dwarf is a very dense solar remnant that is supported by the balance between electron degeneracy pressure and the star’s gravitational self-attraction (3).  A white dwarf’s mass is about that of the sun’s mass but what makes them so interesting is that their size (diameter) is about that of the earth. 
White dwarfs are a very interesting part of stellar evolution.  A white dwarf, when it is first produced, burns at the bottom left of the Hertzsprung-Russel diagram because of this astronomers know that white dwarfs are very hot but not very luminous when they are first produced. As white dwarfs age they begin to cool and if no other forces act on them they eventually become virtually non-existent and they produce no radiation.
White dwarfs are sometimes found in binary systems.  In a binary system two objects (in this case stars) are so close together that they gravitational interact with each other and the gravitational interactions cause the objects to rotate around a common center of mass.  When a white dwarf is found in a binary system typically the second star is a red giant. After sometime the red giant can begin to lose mass, when this occurs the white dwarf accretes matter from the red giant.  If the white dwarf gains enough mass to surpass the Chandrasekhar limit, which is 1.4 solar masses, the electron degeneracy pressure can no longer balance the star’s gravitational self-attraction (3). Thus resulting in a very bright type 1a Supernova (3). 

Above is a Neutron star, I pulses, that's why the image looks the way it does.

            Neutron stars are remnants that form from stars that had initial masses of 4-8 solar masses. These stars go through supernova explosions near the end of there lives and they blow off matter and then form neutron stars of anywhere from 1.4 solar masses to 3.2 solar masses (1).  Neutron stars are supported by neutron degeneracy pressure.  Neutron stars rotate extremely fast when they are first formed, and they later slow down. They rotate fast initially because when the core of a massive star is compressed and it collapses into a neutron star its angular momentum is conserved and the size (diameter) of the star has been reduced to about the size of Ann Arbor. Astronomers have calculated neutron star periods of between 1.4 ms and 30 seconds.  Many astronomers refer to them as pulsars because when observed they appear to pulse because of their very fast periods. A neutron star’s gravitational field is so immense that the escape velocity is approximately 1/3 the speed of light or 10^5 km/s (5).
            Neutron stars can also accrete matter from other objects in space. When neutron stars accrete matter they get smaller as the neutron degeneracy pressure grows more intense.  Neutron stars do have a similar limit to that of white dwarfs but when they reach their limit they behave quite differently (5).  When neutron stars gain matter and neutron degeneracy pressure is over thrown by gravity, a neutron star can form a black hole (5).  

Theoretically this is what a black hole wold look like but of course we can't see a black hole but we can see how other objects are gravitationally effected by it.  Hints the above picture.

Above is a black hole that is gaining mass (accretion) from a star. (That black hole is a thief.....It's stealing all the stars!)

            Black holes are the least common final stage of stellar evolution and the most unexplained stage.  Black holes are a remnant of massive stars around 10-15 solar masses and are formed from the cores of the massive stars after a supernova.  The remnant of 3.2 solar masses or above is left over after the supernova (2). Both electron and neutron degeneracy pressure are not enough to balance the remnants gravity so it collapses.  This collapse produces such a sophisticated entity that not light can even escape it after the event horizon is passed.   
            Black holes, very massive ones, are found at the center of galaxies. The black hole at the center of the Milky Way is about 4.3 million solar masses. There are many black holes bigger than the one found at the center of the Milky Way and there are also smaller ones.  Black holes do not start of very massive (over 8 solar masses), they usually gain matter from objects failing onto them and or they merge with other black holes.  Stars can be tidally disrupted by super massive black holes (5).  When a star passes close enough to a black hole, the black hole can ‘steal’ mass from the star.  This is a very interesting phenomenon and many physicists and astronomers have researched it. 
            The universe is very big and it is comprised of many different objects.  Stars, planets, comets, asteroids, dust, and many other objects populate the universe.  Stars are the most researched part of the universe because there are billion and billions of stars.  Each star depending on its initial mass will either end up as a white dwarf, neutron star, or black hole. 

  1. Neutron Stars and Pulsars. December 2006. Goddard Space Flight Center.
  2. Black Holes.  December 2010. Goddard Space Flight Center.
  3. White dwarfs. December 2006. Goddard Space Flight Center.
  4. Massive Mega-Star Challenges Black hole Theories.  Clara Moskowits. December 18, 2010.
  5. Tidal disruptions from Black holes. Colloquia and class. September 13, 2012. Enrico Ramirez-Ruiz.

Life Cycles of Stars

Lets star out by saying most stars begin there lives in a molecular cloud.  At some point in this cloud when the big "ball" of matter comes together, the matter begins to heat and then it begins to collapse.  As it collapses the cloud becomes more masses because it gains matter from the surrounding accretion disk. 

In the above photo you see the protostar (ball of matter) the bright spot in the middle, and the accretion disk surrounding it.

Ok, now here is the good part. The protostar after it has gained enough mass and is hot enough it will begin nuclear fusion in its core.  The easiest example I can give to explain what nuclear fusion is, is when a star converts hydrogen into helium in its core.

If a star is larger than 200 times the mass of the sun it will not become a star. In simplest terms it blew itself! Also a star less than 0.1 times the mass of the sun will not become a star because it cannot reach high enough forces to begin nuclear fusion in its core.

So if a star is above .1 solar masses and below 200 solar masses, what happens next? It becomes what we know as a main sequence stars.  Main sequence star burn hydrogen into helium in the core.  Depending on how massive the star is it can take billions years to burn through its hydrogen or it could take millions of years. A great example of this is the H-R diagram pictured below.  The stars that are in the like line that looks like a negative slope are those of the main sequence.

The higher the mass (the hotter the star) of the star the faster the star will go through its life cycle.

After stars go through their main sequence stage, they have what we call a helium flash, the outer layers expand and the core contracts.  The star is now exponentially bigger and it is red.  I can use our sun as an example. In 4.5 billion years our sun will complete its main sequence stage and turn into a red giant. When it does everyone will burn to a crisp! The sun will become so big that it will engulf the planet.  So it you are around then please have an escape plan (also look out for other stars from Andromeda because our galaxies will be merging around that time too.).  Oh and if you can get away please take pictures and tag me on facebook!

So after the red giant phase, then it gets a little tricky. For stars around the same size as our sun they will become a planetary nebula they eventually end up as a white dwarf(I will do a post of deaths of stars). 

For stars much much more massive than our sun, the stars will go supernova and blow up and later become a neutron star or black hole.

Friday, September 28, 2012

Star Formation

There are billions and billions of stars in our Universe, but a big question that many people ask is were do these stars come from and how are they formed. Well I am about to give some general information on star formation.

Stars form in molecular clouds, also refereed to as star nursery's because star formation occurs within them, that are dense enough to allow the formation of molecules. The most common molecule being Hydrogen seeing as how hydrogen makes up about 75%, of the universe's baryonic (ordinary) matter.

Molecular Cloud:

In these clouds turbulence or fluctuations make it so a certain amount of matter in the cloud can join together then gas and dust in the cloud begin to collapse under its gravitational attraction.  As it begins its collapse, the material in the center starts to get hotter.  This core of hot material is what we call a protostar.


A protostar cannot be called an "official" star until it begins nuclear fusion in its core.   Nuclear fusion begins when a protostar begins converting hydrogen into helium.

Stay tuned for the life cycle of a stars!!
On September 27, 2012 Jeff Oishi joined the University of Michigan Astronomy department to present his data on accretion disks.

Jeff Oishi is a theorist with a broad interest in Astrophysical fluid dynamics. I know that sounds very complicated but in simpler terms he likes to research the natural ways that fluids flow and move in terms of astronomical objects.

He received his Bachelor of Science in Applied Physics from Columbia University in 2000. In 2007, Oishi received his PhD in Astronomy from the University of Virginia. 

 If you want more information on Oishi here is a link to a site with some of his research

Oishi presented his research on black holes this past Thursday to the University of Michigan astronomy department.  He seemed to be particularly focused on accretion disks and how they influenced star formation (I WILL DO A POST ON STAR FORMATION AND ONE ON STAR TYPES SO YOU CAN LOOK THERE FOR INFORMATION ON STARS.)  An accretion disk is a structure that is formed by diffuse material (gas and dust) that is in orbital motion (the way the earth rotates around the sun) around a central body. In Oishi's case the central body was a protostar. 

Here are some images of accretion disks:

These accretion disks (the dust inside them), according to Oishi, rotate around the protostar just as the earth rotates around the sun. But, some of the disks matter actually can fall onto the protostar, thus making it bigger and more massive. 

Oishi researches the material in the accretion disks and how that material behaves. He said that he studied the composition of the disks. The density of the disks.  He also studies the fluctuations in the disk.  He says that all of the matter in the disk is not setup in a homogenous way.  The matter can be unevenly distributed throughout the accretion disk. 

Here is an image of a magnetic field in an accretion disk:

All in all it was a great presentation that was very interesting.

Tuesday, September 25, 2012

The 16th annual Astronomy at the beach was hosted this past Saturday (9/22).  It was hosted by Kensington Metropark and the Great Lakes Association of Astronomy Clubs (GLAAC). It was fun and exciting. At Kensingston park hundreds of people gathered to come out and participate. There were telescopes lined up all around the lake, there were 3D presentations, and there was a keynote speaker. 

Let me start by saying that even though it was an extremely cold outside and that it is totally probably that I caught a cold during that night......It was all worth it.  The speaker was an astronaut. A real astronaut.  He came in wearing a blue NASA jump suit and I even got to shake his hand!!!!

The keynote speaker was Dr. Andrew J. Feustel.  He is a geophysicist from Lake Orion, Michigan.  He went to Oakland Community College and Purdue University. He participated in two NASA missions in 2006 and 2009. Both times his family could not see him land. The first time was because the weather conditions didn't permit it and the second was because it was night when the space shuttle landed.  Feutsel spoke about both his missions and he showed video of himself and the space ship crews in space. I have to say that the videos they made, made space travel look sooooo fun! I guess the fun of making the videos made up for the intense raining he had to do in order to get ready for the missions.  Also he told us that he and his crew members assembled the final parts of the international space station and all i could think of was wow I shook hands with someone that will go down in history!

Here is a picture of Dr. Andrew Feutsel, he was the perfect speaker for Astronomy at the beach and he made a cold night awesome. Google him for more information or use this link He seemed like a pretty awesome guy.

Sunday, September 23, 2012

September 20, 2012 Colloquia

On Thursday September 20, 2012 the astronomy department had an exciting and engaging Colloquium. Wendy Freedman, presented data on two projects she participated in. The first was the CSP and the second the CHP. 

Wendy Freedman has been a frequent guest speaker at the University of Michigan she comes on average once every three years.  Freedman graduated from the University of Toronto in 1984 with her Ph.D. She now works at Carnegie and in 2009 she won the Gruber Cosmology Prize.

She spoke on her and her colleagues work on the Carnegie Supernova and Hubble Constant Project (hints the CSP and CHP). She focused mostly on the current cosmological model, dark energy, Hubble's Constant (Ho) and the Carnegie Supernova project.

She gave detailed information about the Friedman equation and the cosmological framework (Einstein's tension vs. energy momentum tension)

Freedman showed that the current concordance model states that Ho = 72 + or - 5 km/sec/Mpc, but according to her and her colleagues work at Carnegie the newly estimated value of Ho = 73.8 + or - 2.4 km/sec/Mpc. 

This is a huge break through and she is going to study further into it with the CSP-I which began in 2011 and will run for seven years in total according to her. So be on the look out for updated values of Ho and keep up to date on how the CSP project is progressing.