Podcaster: Richard Drumm
Title: Space Scoop: A Monster in the Middle
Organization: 365 Days Of Astronomy
Link : astrosphere.org ; http://unawe.org/kids/unawe1547/
Description: Space scoop, news for children.
Bio: Richard Drumm is President of the Charlottesville Astronomical Society and President of 3D – Drumm Digital Design, a video production company with clients such as Kodak, Xerox and GlaxoSmithKline Pharmaceuticals. He was an observer with the UVa Parallax Program at McCormick Observatory in 1981 & 1982. He has found that his greatest passion in life is public outreach astronomy and he pursues it at every opportunity.
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Transcript:
This is 365 Days of Astronomy. Today we bring you a new episode in our Space Scoop series. This show is produced in collaboration with Universe Awareness, a program that strives to inspire every child with our wonderful cosmos.
Today’s story is:
A Monster in the Middle
The Universe is mostly just empty space. The nearest star to our Solar System is 40 trillion kilometers away (that’s 40 million, million!). Aboard the fastest rocket we have today, it would take almost 80,000 years to travel there. To reach distant stars and galaxies it would take many millions of years longer.
This pretty much rules out space travel as a way to study cosmic objects. So, how can we study the stars?
…Well with telescopes, of course! Telescopes are the only tools we have to study the distant Universe.
In a way, when we look at distant stars with our telescopes it’s like we are traveling to them at the speed of light. All from the comfort of home.
However, some night sky investigations need many months of observing. Imagine sitting looking through a telescope for day after day, month after month — it would be beyond boring. Instead, clever scientists at LCOGT, the Las Cumbres Observatory Global Telescope network came up with a better option — robotic telescopes.
A Robot is a machine controlled by a computer. Robots can be taught to do many different things without human involvement, like dance, clean a carpet or even control a telescope! Robotic telescopes are the perfect tools for carrying out time-consuming studies of space.
LCOGT is a group of robotic telescopes located in six different countries. Using the LCOGT network scientists have been carrying out studies on several “active galaxies”.
Active Galaxies are fantastically bright. But not all the light comes from the billions of stars in the galaxy; most of it comes from the very heart of the galaxy, where a supermassive black hole is feeding.
For one of the studies the telescopes watched an active galaxy called Arp 151 for 200-days straight! The results were amazing and the team was able to complete a notoriously difficult task – weighing a black hole.
Here’s how they did it.
It’s called “reverberation mapping” and it relies on the fact that the SMBH, the super massive black hole has a disk of matter that’s falling into the hole and is emitting a boat-load of light.
So before the matter falls into the black hole it gets hot as all heck and shines brightly. The light from here is radiating outward and hits clouds of gas called a Broad Line Region or BLR that are farther out from the SMBH, just past the accretion disk and that light then bounces off the BLR clouds and is seen in our telescopes.
The light from the SMBH is variable because there are lumps in the accretion disk of infalling material. Basically the innermost parts of the disk flicker irregularly. The light takes time to reach the BLR, on the order of a week or two and then the BLR clouds also flicker irregularly. This is the “Reverberation” that we’re mapping. Somewhat like a very small, unresolved light echo.
Thus we can determine the distance from the SMBH to the BLR using the speed of light in the calculation.
These BLR clouds orbiting the SMBH are moving very fast and as a result the spectral lines in that light get red shifted as the gas moves away from us on one side of the accretion disk and blue shifted as it moves toward us on the other side.
This mix of red and blue shifting of the spectral lines causes the lines to be wider than they would be if the source of the light was stationary. This is where the term “Broad Line Region” comes from. From the width of the lines we can calculate how fast these BLR clouds are orbiting the SMBH. In other words, the orbital period.
So let’s recap.
We know how far out the orbiting BLR clouds are and how fast they are orbiting the black hole. Using Kepler’s 3rd law we need only:
1. The orbital period of the clouds. Which we have.
2. The Gravitational Constant. Which we have.
3. The distance from the SMBH to the clouds.
Which we also have.
Plug the numbers into Kepler’s equation and solve for the mass of the SMBH and there you have it!
They found that the black hole lurking in the center of Arp 151 is 6.2 million times the mass of our Sun! That’s one heavyweight monster! The SMBH that is in the center of our Milky Way Galaxy is 4.1 to 4.3 million solar masses, 2/3 the size of Arp 151’s.
Here’s a Cool Fact:
The LCOGT network uses robotic telescopes that need no human operators to control them. Our word “robot” comes from the Czech word “robota” which means “forced labor.” Most robots today are used for boring, repetitive actions or jobs considered too dangerous for humans.
For example, a robot is ideal to send into a building that has a possible bomb in it or to explore the harsh landscape of an alien planet. In fact we know of one planet that is inhabited solely by robots. We call it Mars…
Thank you for listening to 365 Days of Astronomy!
End of podcast:
365 Days of Astronomy
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