November 6, 2012
Astronomers Detect Bright Flare-up In Our Black Hole
Lee Rannals for redOrbit.com — Your Universe Online
A team of scientists say they have detected the brightest flare ever observed in our galaxy's black hole.
The black hole is considered to be low-key, emitting very little energy for its size. It gives off about as much energy as the sun, despite it being 4 billion times as massive.
The recent flare is 150 times brighter than the black hole's normal luminosity. Scientists observed the flare for more than one hour before it faded away. This brief burst of activity could be a clue to how mature black holes like Sagittarius A* behave.
“We´re learning what black holes do when they´re old,” Joey Neilsen, a postdoc at MIT´s Kavli Institute for Astrophysics and Space Research, said in a statement. “They´re no young whippersnappers like quasars, but they´re still active, and how they´re active is an interesting question.”
Astronomers detect black holes by the light energy given off as they consume nearby matter. The centers of newborn galaxies and quasars can appear extremely bright, giving off massive amounts of energy as they eat up their surroundings.
“Everyone has this picture of black holes as vacuum sweepers, that they suck up absolutely everything,” Frederick K. Baganoff, a research scientist at MIT Kavli, said in a statement. “But in this really low-accretion-rate state, they´re really finicky eaters, and for some reason they actually blow away most of the energy.”
To detect the black holes, the team obtained images of the black hole from Chandra, and utilized the telescope's High Energy Transmission Gratings Spectrometer (HETGS). This instrument is able to analyze the incoming light.
The spectrometer onboard Chandra split the black hole's X-rays into various wavelengths, similar to the light that passes through a prism. The team analyzed the data and found a spike of 700 photons.
“Suddenly, for whatever reason, Sagittarius A* is eating a lot more,” Michael Nowak, a research scientist at MIT Kavli, said in the statement. “One theory is that every so often, an asteroid gets close to the black hole, the black hole stretches and rips it to pieces, and eats the material and turns it into radiation, so you see these big flares.”
Nowak believes that flare-ups occur more frequently than scientists expected. The team reserved more than a month of time on Chandra to study Sagittarius A* in order to identify more flares.
Mark Morris, a professor of astronomy at the University of California at Los Angeles, said while less flares take place daily, scientists have detected very few events from the black hole as bright as the recent one.
“These bright flares give information on the flaring process that isn't available with the weaker ones, such as how they fluctuate in time during the flare, how the spectrum changes, and how fast they rise and fall,” Morris said in the statement. “The greatest importance of this bright flare may be that it builds up the statistics on the characteristics of strong flares that can eventually be used to [identify] the cause of such flares.”