Oct 2: The Glorious Past of Our Monster Black Hole

Last week, physics graduate student and NASA fellow, Shuo Zhang, introduced us to the monstrous black hole in the center of our galaxy. It is well established that every massive galaxy hosts a supermassive black hole in its center and Milky Way is not an exception. Astronomers analyzing the orbits of stars in the galactic center, enabled by advancements in observing technology, realized that the only feasible scenario for the dark object in the center is the galaxy is a black hole with mass of a few million times the mass of the sun.

The black hole is known as Sagittarius A-star (SgrA*), since it is located near the border of the constellations Sagittarius and Scorpius. Being the closest supermassive black hole we can observe, SgrA* is of great astronomical interest. But is it a typical black hole? SgrA*, is one of the quietest supermassive black holes among all the nearby galaxies. However, that wasn't always the case. Recently, the Fermi Gamma-ray Space Telescope discovered a bubble of gamma-rays surrounding our galaxy, which indicate that 2 million years ago, the black hole was very active, swallowing gas and expelling in at large distances. 

Shuo also mentioned her own work observing the black hole at the center of the galaxy with an X-ray telescope called NuSTAR (a NASA mission, in which Shuo's research group here at Columbia was a major contributor). Shuo observes sporadic X-ray flares, which last for a few seconds. During these flares the black hole becomes hundreds of times brighter and then returns to its quiet state. The origin of the flares is still unknown and it has been suggested that we observe the heated remnants of an asteroid that was ripped apart by SgrA*.

Unfortunately, the weather did not cooperate to allow stargazing. Whoever stayed after the lecture had a chance to see 3D movies of the galaxy lead by undergraduate student Richard Nederlander, or hear a short presentation by graduate student Emily Sanford, about the exciting discovery of water on the surface of Mars.

-- Maria Charisi (graduate student)

October 5: X-ray Spectacular!

On October 5th, over 175 people came to Doug Thornhill's talk on the newly launched X-ray telescope NuSTAR. NuSTAR was assembled at the Nevis Laboratories of Columbia University and Doug worked with the NuSTAR team for almost four years as an undergraduate student at Columbia since the beginning of the project. He provided a clear and thorough explanation on how x-ray telescopes work, with a physical demonstration on how light is detected by the telescope. Doug then showed how NuSTAR was built and discussed the scientific goals of the telescope including the survey of super-massive black holes, supernovae remnants and compact objects, as well as the study of the energy transport of our sun.

After the talk, some people stayed in the lecture hall to enjoy the movie "High Energy Vision: The Chandra X-ray Observatory," which is another NASA X-ray telescope launched more than a decade ago. 

As it was a fairly clear night, many people headed up to the roof to view the night sky through the telescopes. Additionally, Columbia undergrad, Bryan Terrazas, showed 3D movies on the 13th floor. 

Join us for our next event on October 19th, when we will hear from Or Graur on how astronomers use the universe as their laboratory.

--Yuan