Editor's note: Brian Williams is a space enthusiast and writer living in Salinas, California.
NASA’s Nuclear Spectroscopic Telescope Array, called NuSTAR, has taken its first glimpse of our galaxy’s supermassive black hole, thanks to a recent flare-up at the galactic core.
NuSTAR, a state-of-the-art, space-based X-ray telescope, was aimed at Sagittarius A*, a compact radio source identified as a black hole, for two days in July. The goal was to better understand just what makes our galaxy's central black hole so different from others.
Compared to other galaxies, the Milky Way’s black hole is relatively calm. While other supermassive black holes devour gas and stars around them, releasing large amounts of energy in the process, ours only seems to have the occasional light snack, showing just a bit of activity as matter is consumed: the tell-tale burst of energy seen in X-ray and radio emissions.
According to Fiona Harrison, NuSTAR’s principal investigator at CalTech in Pasadena, California, fortuitous timing plays no small role in observing the activity.
“We got lucky to have captured an outburst from the black hole during our observing campaign. These data will help us better understand the gentle giant at the heart of our galaxy and why it sometimes flares up for a few hours and then returns to slumber," she said in a written statement.
Thanks to the instruments aboard NuSTAR, the team was able to see the X-rays created by matter being heated up to approximately 180 million degrees Fahrenheit (or 100 million degrees Celsius) in regions where particles are accelerated close to the speed of light.
"Astronomers have long speculated that the black hole's snacking should produce copious hard X-rays, but NuSTAR is the first telescope with sufficient sensitivity to actually detect them," team member Chuck Hailey of Columbia University said in a written statement.
Fred Baganoff, a NuStar team leader at the Massachusetts Institute of Technology, stressed in an e-mail the importance of the NuSTAR data for getting a clearer picture of the dark heart of our galaxy.
“Understanding such a complex and alien environment from so far away is like piecing together a jigsaw puzzle when you do not know what the final image should look like; most of the pieces are missing and the whole puzzle is too small and far away to be seen by the human eye. What NuSTAR has done is give us more of the pieces. Until 2000, the only pieces we had were on the left-hand side of the puzzle in the radio and millimeter wave bands, where Sagittarius A* had been studied since its discovery in 1974. The entire right-hand side of the puzzle, visible only in the soft X-rays, hard X-rays and gamma-rays, was completely missing. ... The center of the puzzle was missing, too, since vast clouds of gas and dust completely block our view of the center of our galaxy in optical and ultraviolet light. Only one in a trillion optical photons makes it through that dark haze.”
Taken with data from other observatories (NASA’s Chandra X-ray Observatory and the W.M. Keck Observatory in Hawaii were also pointed at Sagittarius A*), scientists hope NuSTAR can shed light on the activity cycles and evolution of black holes. There is also a wealth of non-black hole related data that the X-ray space telescope will help scientists understand, Harrison said.
“NuSTAR will look at a wide range of phenomena from exploding stars to neutron stars and black holes. NuSTAR will even study our own sun!”
Four months into its two-year mission, NuSTAR is off to a promising start. Launched in June 2012, NuSTAR’s mission is to conduct a survey of black holes throughout the universe that are millions of times more massive than our own sun. As for what's next for NuStar, Harrison said it is working on other targets.
“NuSTAR has already moved on to look at the evolving remnant of a supernova explosion that happened in 1987 nearby, in the Large Magellanic Cloud (a satellite of the Milky Way) called SN1987A. NuSTAR will next look at very luminous objects in nearby galaxies, called ultraluminous X-ray sources. The source of their X-ray brilliance is not understood. NuSTAR looks at a new target every few days.”