Planet-hunting satellite observes supermassive black hole

Joner in the observatory at BYU's Eyring Science Center.

If you want to see just how far BYU's latest research extends, step outside of your house tonight, look up towards the sky, focus your view between the constellations of Cygnus and Lyra, and then zoom in about 100 million light years.

That's the home of a galaxy known as KA 1858, which contains a black hole that BYU scientists observed with the help of NASA and other astrophysicists throughout the University of California system.

The study, which appears in the Astrophysical Journal, estimates that this black hole has a mass of approximately 8 million times the mass of our sun.

Originally, the NASA Kepler satellite's main mission is to hunt for earth-like planets in our own galaxy. In this study, however, researchers were able to combine data from the Kepler mission with ground-based data to observe black hole characteristics. Many of the ground-based observations were performed at BYU's West Mountain Observatory, the largest research observatory in Utah.

"It was a long project that involved lots of different observers, some of them around the world," said Professor Michael Joner, co-author of the study. "Using measurements that were done at BYU, we were able to determine that the mass of the central black hole for this galaxy was about 8 million times the mass of the sun -- that's a really really massive object."

Astronomers are used to measuring light radiated by different type of objects, and black holes are very difficult to measure because they don't give off any radiant energy. For this reason, Joner and masters student Carla Carroll, who is also a co-author of the study, used a method known as reverberation mapping.

Reverberation mapping involves observing the light that is emitted as material spirals toward the black hole. At different distances from the center, the light interacts with nearby gases, which then re-emit that light. These groups of light reach the ground-based telescope within a few days of each other. By analyzing this time difference and by measuring how fast the material is moving around the center of the galaxy, they were able to determine the mass of this central black hole.

According to Carroll, current techniques for this method require some of the largest, and quite overbooked, telescopes in the world. She and Joner are working on a way to use smaller telescopes that have the abilities to observe different active galaxies. This way, astrophysicists everywhere can have the ability to do this science using smaller and less costly telescopes.

"After lots of collaboration, we were both learning amazing things and coming up with new ideas and possibilities," Carroll said. "The best part of this project for me was learning about active galactic nuclei and supermassive black holes on a level I never could have in either undergraduate or graduate classroom settings."

Carroll is finishing up a similar project to the publication and will graduate in April 2015 with a Master of Science. She recently earned admission to the University of Heidelberg in Germany for a Ph.D. program in astrophysics.

Mentored research opportunities are a big reason why BYU is ranked so highly as a Ph.D. launch pad. According to the National Science Foundation, BYU ranks fifth in the country for number of graduates who go on to receive doctorate degrees.

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Record-breaking black hole outburst detected

An image of a simulation of the gas cloud’s encounter with Sgr A*. The blue lines mark the orbits of the so-called “S” stars that are in close orbits around the supermassive black hole.

Last September, after years of watching, a team of scientists led by Amherst College astronomy professor Daryl Haggard observed and recorded the largest-ever flare in X-rays from a supermassive black hole at the center of the Milky Way. The astronomical event, which was detected by NASA's Chandra X-ray Observatory, puts the scientific community one step closer to understanding the nature and behavior of supermassive black holes.

Haggard and her colleagues discussed the flare today during this year's meeting of the American Astronomical Society in Seattle.

Supermassive black holes are the largest of black holes, and all large galaxies have one. The one at the center of our galaxy, the Milky Way, is called Sagittarius A* (or, Sgr A*, as it is called), and scientists estimate that it contains about four and a half million times the mass of our Sun.

Scientists working with Chandra have observed Sgr A* repeatedly since the telescope was launched into space in 1999. Haggard and fellow astronomers were originally using Chandra to see if Sgr A* would consume parts of a cloud of gas, known as G2.

"Unfortunately, the G2 gas cloud didn't produce the fireworks we were hoping for when it got close to Sgr A*," she said. "However, nature often surprises us and we saw something else that was really exciting."

Haggard and her team detected an X-ray outburst last September that was 400 times brighter than the usual X-ray output from Sgr A*. This "megaflare" was nearly three times brighter than the previous record holder that was seen in early 2012. A second enormous X-ray flare, 200 times brighter than Sgr A* in its quiet state, was observed with Chandra on October 20, 2014.

Haggard and her team have two main ideas about what could be causing Sgr A* to erupt in this extreme way. One hypothesis is that the gravity of the supermassive black hole has torn apart a couple of asteroids that wandered too close. The debris from such a "tidal disruption" would become very hot and produce X-rays before disappearing forever across the black hole's point of no return (called the "event horizon").

"If an asteroid was torn apart, it would go around the black hole for a couple of hours -- like water circling an open drain -- before falling in," said colleague and co-principal investigator Fred Baganoff of the Massachusetts Institute of Technology in Cambridge, MA. "That's just how long we saw the brightest X-ray flare last, so that is an intriguing clue for us to consider."

If that theory holds up, it means astronomers have found evidence for the largest asteroid ever to be torn apart by the Milky Way's black hole.

Another, different idea is that the magnetic field lines within the material flowing towards Sgr A* are packed incredibly tightly. If this were the case, these field lines would occasionally interconnect and reconfigure themselves. When this happens, their magnetic energy is converted into the energy of motion, heat and the acceleration of particles -- which could produce a bright X-ray flare. Such magnetic flares are seen on the Sun, and the Sgr A* flares have a similar pattern of brightness levels to the solar events.

"At the moment, we can't distinguish between these two very different ideas," said Haggard. "It's exciting to identify tensions between models and to have a chance to resolve them with present and future observations."

In addition to the giant flares, Haggard and her team also collected more data on a magnetar -- a neutron star with a strong magnetic field -- located close to Sgr A*. This magnetar is undergoing a long X-ray outburst, and the Chandra data are allowing astronomers to better understand this unusual object.

As for the G2: Astronomers estimate that the gas cloud made its closest approach -- still about 15 billion miles away from the edge of the black hole -- in the spring of 2014. The researchers estimate the record breaking X-ray flares were produced about a hundred times closer to the black hole, making it very unlikely that the Chandra flares were associated with G2.

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