Edwin Hubble is a heroic name within the field of astronomy.
“Hubble’s research provided the foundation of extragalactic astronomy as we know it today,” Bradley Peterson, department chair for astronomy at Ohio State, said. “He was without a doubt the most important observational astronomer of the last century.”
Edwin Hubble’s remarkable observations throughout the 1920’s led to the conclusion that the Milky Way Galaxy was not the only galaxy within the universe, and that the new and improved multi-galactic universe was expanding.
In April of 1990 the Hubble Space Telescope was placed into orbit. This telescope was named after Hubble in honor of his outstanding contributions to science.
For the past 12 years Dr. Chris Kochanek, a faculty member of Ohio State’s astronomy department and an Ohio Eminent Scholar, has been using Hubble to conduct his work on quasars.
“A quasar is a huge black hole a million to a billion times heavier than the Sun that eats gas,” Kochanek said.
Kochanek’s research involves applying the technique of gravitational lensing to try and obtain a size for the accretion disk of distant quasars.
“The machine for getting the gas down to the black hole is called an accretion disk, which is a relatively thin hot disk of gas orbiting the black hole,” he said.
“But we need a telescope with a million times the resolution of even the Hubble Telescope to get a picture of one. So we combine Hubble with Einstein’s Telescope, using the way gravity bends light, to beat the system,” he said.
Massive objects, such as stars and galaxies, are capable of bending the light from more distant objects. The light is bent due to the massive objects’ gravitational influence on the light. This process is known as gravitational lensing.
“Using the rare quasars lying behind a foreground galaxy, we use the gravity of the stars in this galaxy to resolve the disk and measure its size,” Kochanek said.
Kochanek uses the Advanced Camera for Surveys, which is one of the instruments attached to Hubble. One of ACS’s capabilities is that it provides data within the ultraviolet (UV) wavelength range, which is what Kochanek is interested in. The UV information he obtains from Hubble provides him one of the pieces for his puzzle. He also collects X-ray data from the Chandra X-Ray Observatory (satellite).
“If you want to look very close to the black hole you have to look at it in the X-Rays and ultraviolet light, and you can only do this from space using the Chandra or Hubble Telescopes,” Kochanek said.
So, what is so important about learning the size of the accretion disk for a quasar that is billions and tens of billions of light years away?
“Theoretical calculations are being applied towards computational simulations to try and reproduce the behavior of a quasar. The physics that goes into describing a quasar is extremely complicated. The devil is in the details, and one of the important parameters includes how close to the center you decide to place the accretion disk,” Kochanek said.
“Dr. Kochanek’s research is part of the ongoing search to obtain a concrete understanding of quasar behavior,” Peterson said. “Quasars are some of the most distant and therefore oldest objects, ever observed, and they provide a key link for understanding the emergence of structure within the universe.”
