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 (http://michastrostudent.blogspot.com/2012/10/dwarf-galaxies.html) and how they can be used to determine the composition of dark matter (http://michastrostudent.blogspot.com/2012/10/dark-matter.html).

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. http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
2. Dark Matter. http://csep10.phys.utk.edu/astr162/lect/cosmology/darkmatter.html
3. The neutrino and its friends. Dave Casper. http://www.ps.uci.edu/~superk/neutrino.html
4. WIMPs. Dave Spergel. March 6 1996. http://www.astro.princeton.edu/~dns/MAP/Bahcall/node8.html
5. Gravitational lensing. Jcohn. Berkley. Dec 13, 2010. http://astro.berkeley.edu/~jcohn/lens.html
6. Gravity Lens reveals dark matter. Bob Swarup. Aug 25, 2006. http://physicsworld.com/cws/article/news/2006/aug/25/gravity-lens-reveals-dark-matter

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 http://research.pbsci.ucsc.edu/astro/faculty/

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! :)

October 4, 2012. Michael Eracleous

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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).

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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:
 http://www.youtube.com/watch?v=ZIX2ngAwEn0

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.

Quasar:

Blazar:

 Seyfret:

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.