Does this accretion disk make me look fat?
Black holes may hold the key to how our universe evolved, but only if scientists can determine their exact masses. To get more accurate measurements of distant black holes, astronomers are using robots to monitor the glow of black hole accretion disks — a disk of material emitting energy as it falls into the black hole.
The idea behind this endeavor is that the matter (space dust and gas) in the accretion disk at the mouth of an active black hole will light up distant clouds. A technique known as reverberation mapping chemically analyzes the gas in the disk around the black hole and compares it with the glow of gas farther away. By doing this, astronomers can determine the mass of the black hole and therefore the strength of its gravitational field.
“This technique takes advantage of the fact that accretion disks don't always shine at the same brightness,” the University of Texas McDonald Observatory wrote on its Stardate.org website, according to Discovery News.
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“A disk can flare brightly as new material falls in […] or as magnetic fields cause some of the disk's gas to clump together. Measuring how long it takes the surrounding clouds to brighten as they are illuminated by these flares reveals their distance from the black hole. And measuring the width of the lines in the spectra from these clouds reveals how fast they are moving,” the observatory said.
To test whether robots would be able to create the maps desired by astronomers, a pilot project was conducted at the Las Cumbres Observatory Global Telescope Network (LCOGT) — which consists of 11 automated telescopes in Texas, Hawaii, Australia, South Africa and Chile. At the Faulkes Telescope North and South locations, located in Hawaii and Australia respectively, a pair of light-splitting spectrographs called FLOYDS was recently installed.
FLOYDS was named after the band Pink Floyd in honor of the light-splitting prism on the cover of the “Dark Side of the Moon” album.
“A spectrograph is a special kind of camera that splits the light of an object into its constituent colors, like a rainbow, and lets you do things like measure the chemical composition of an object and how fast it is moving with respect to you,” astrophysicist David Sand, with Texas Tech University, wrote in an email to Discovery News.
For 200 days, the FLOYDS spectrograph in Hawaii monitored Arp 151 — a galaxy about 300 million light years away in the constellation Ursa Major. This galaxy has been studied extensively, since it contains a massive black hole, and previous reverberation mapping projects determined the mass of the black hole to be between 6.5 and 7 million times the mass of our sun.
After the 200 days were up, the robots determined Arp 151 to have a mass of 6.2 million times the mass of our sun, proving the robots are able to properly map the black hole.
Astronomers are now hoping to complete larger surveys of nearby and more distant galaxies with active black holes. “We’re really going to try to push the technique into new regimes with our robotic capabilities,” Sand said.
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