NuSTAR Spies Ravenous Black Holes
Among the first targets netted by NuSTAR, a high-energy X-ray telescope launched in June, is this stunning spiral galaxy IC342, also known as Caldwell 5, located 7 million light-years away in the constellation Camelopardalis (the Giraffe.)
NuStar’s data is pictured in magenta and superimposed on an optical image showing the galaxy’s spiral arms, stars, dust and gas.
“Previous observations of the same galaxy taken in high-energy X-rays amounted to only 1 pixel, so we couldn’t resolve these two light sources,” NuSTAR lead scientist Fiona Harrison, with the California Institute of Technology, told reporters during a press conference webstreamed from the American Astronomical Society meeting in Long Beach, Calif.
The two magenta spots are “astonishingly bright, ultra-luminous black holes that are feeding,” Harrison said.
The objects appear about 10 times brighter than typical stellar-mass black holes, similar to those found throughout the Milky Way galaxy. But they aren’t believed to be supermassive black holes because they are not located at their galaxy’s center.
That leaves two possibilities. One, the objects are intermediate-mass black holes, with 500 to 2,000 times the mass of the sun. “If that’s the case, we really have no idea how they formed,” Harrison said.
Second, the black holes may be smaller, but feeding, making them extremely bright in X-ray light.
“The physics going on here may be different than what’s going on in stellar-mass black holes in our galaxy,” Harrison said.
Scientists plan to take the data from NuSTAR and compare it with observations from NASA’s Chandra X-ray Observatory and other X-ray telescopes to get a broad-brush look at all the X-ray light streaming from known stellar-mass black holes in the Milky Way.
“Do the physics just scale up, or is there new physics going on?” Harrison said.
The NuSTAR team also released a new view of the supernova remnant Cassiopeia A, below.
The highest energy X-rays are in blue. Background stars are courtesy of the Digitized Sky Survey.