UCLA Planetarium Journey to the Center of the Milky Way UCLA Galactic Center Group -- group of astronomers that look at the center of our galaxy. UCLA Planetarium Created by Jessica Lu

Galactic Center 30,000 light years COBE Image Image 1 The Milky Way - Point out Solar System Milky Way is a spiral galaxy About 30,000 light years from the galactic center Image 2 You can see the milky way -- a creamy strip across the sky We see Milky Way edge on (like edge of a plate) When you look at the night sky, all the stars you see are a small part of our own Milky Way galaxy. The Milky Way is a spiral galaxy, and the sun is located about 30,000 light-years from the Milky Way’s nucleus on the Orion arm. If you see a creamy strip across the sky on a moonless night, you’re looking out at the outer edge of the Milky Way. During the summer, you can look towards the constellation Sagittarius and look at the center of the Milky Way. 1. Like all galaxies, the Milky Way is held together by gravity. This gravity also holds the stars, gas, and dust in orbit around the center of the galaxy. Just as the planets orbit around the sun, the sun orbits around the center of the Milky Way. Of course, it’s a long trip around—about 225 million years! As we journey into the galactic center, remember that the time it takes to orbit (travel all the way around) gets shorter and shorter. 2. The second image is what we actually see of the Milky Way for our solar system. We see our galaxy edge on. COBE Image 30,000 light years

Radio Sub-mm Mid-IR Near-IR Optical X-ray Image 1 Edge on Milky Way is obscured by dust Image 2 Zoom in to Galactic Center Note Dark Lane… this isn’t fewer stars, but more dust Look into night sky towards constellation saggitarius Image 3 To see Galactic Center, we need to consider other wavelengths of light (types of light) Note Optical is dark (can’t see through dust) Note Radio, Infrared, X-ray First lets look in radio… next slide The Galactic Center is obscured from our view by a prodigious amount of absorbing gas and dust that lies along the 25,000 light year (2.5X10^17 mile) distance from there to our Sun. As a result, most of what we know about this part of our galaxy comes from observations of radio and infrared radiation, whose long wavelengths can pass through the dense absorbing medium and reach our telescopes on Earth. 2. A blown up map so you can find the Galactic Center yourself. It is located near the constellation Sagittarius. (27 by 40 degrees) 3. Because it is so difficult to see things in the Galactic Center at optical wavelengths, we need to consider other wavelengths. Radio, Sub-mm, Mid-IR, Near-IR, X-ray. Each provides a different window. First lets look in the radio (next slide).

Very Large Array (VLA) radio telescope in New Mexico. Image from the Very Large Array (VLA) radio telescope in New Mexico. Radio Image of Galactic Center (1500 x 2500 light years) Few degrees on a side Image from the Very Large Array in New Mexico Note filaments, supernova remnants (explain) Brightest spot is towards the galactic center. Try looking in X-ray next …. Next slide. This image was produced by the VLA and is a good representation of the wide variety of phenomena occurring at the Galactic Center. The two most prominent features are the non-thermal and thermal radios arcs or "filaments" and a collection of ring-shaped supernova remnants (SNRs). At the other end of the spectrum, we can look at X-ray images (next slide).

Chandra X-ray Space Telescope Image of the Galactic Center X-ray image of Galactic Center (400 x 900 light year) Taken with Chandra space telescope Seeing white dwarf stars, neutron stars, black holes All swimming in hot gas many millions of degrees. Brightest white patch in the center holds a supermassive black hole. Now lets look in the infrared…. Next slide This 400 by 900 light-year mosaic of several Chandra images of the central region of our Milky Way galaxy reveals hundreds of white dwarf stars, neutron stars, and black holes bathed in an incandescent fog of multimillion-degree gas. The supermassive black hole at the center of the Galaxy is located inside the bright white patch in the center of the image. The colors indicate X-ray energy bands - red (low), green (medium), and blue (high). Chandra X-ray Space Telescope Image of the Galactic Center

2MASS Infrared Images of the Galactic Center Notice that all these points are stars… very crowded. This covers 1.9 x 1.9 square degrees (hit enter to zoom again) This covers 0.6 x 0.7 square degrees (hit enter to zoom again) This covers 6.8 x 6.7 square arcminutes Note the brightest point of the last image… almost a spirally looking structure Lets look in the radio again now that we are zoomed in… next slide

Radio image (~ 3 arcmin on a side) Note the shell of gas Note the mini-spiral… this is hot gas within 1-2 parsecs (30-65 light years) of the supermassive black hole. Taken (again) with the very large array in New Mexico They can actually move the telescopes around on train tracks. Back to infrared where we can see the stars… next slide.

Image 1: 80’’ by 80’’ image (just the mini-spiral) Taken with the Keck Telescope This was just a quick snapshot… lets zoom in and look deeper Image 2: A deeper look reveals many more stars. This is a Gemini telescope image (JHK). Notice the bowshock… a star plowing through surrounding gas and dust (just like a ship through water) Notice the clustering of very bright stars… this is towards the black hole Image 3: Another image taken with Keck (KL’) Fantastic detail… bright stars, dim stars, hot gas Point out region where black hole lives. We can only get these very detailed images with something called Adaptive Optics.

Atmosphere makes stars look blurry (just like stones through running stream) Adaptive optics uses a bright optical star to correct for this blurring. Galactic Center doesn’t have a bright optical star close by (remember obscuring dust) Instead, we shine a laser into the sky to “create” a bright star Box is region where the black hole is located… notice all the stars. We have looked carefully at this region for 10 years… How did we find the supermassive black hole? next slide

Over 10 years, the stars moved around Just like planets orbit the sun, these stars were orbiting something VERY BIG From these orbits, we found a supermassive black hole that was 4 million times the mass of our Sun. Can we see the black hole itself??? Next slide.

In fact, we can see the black hole. Movie of the black hole gobbling up material (gas). Lunch, dinner, afternoon snack… What does the black hole look like? … next slide

Black hole might look something like this… (artists rendition). A disk of gas which slowly falls onto (or accretes) the black hole Watch movie of black hole.

UCLA Planetarium Journey to the Center of the Milky Way Created by Jessica Lu