Text Size

NASA's Swift Satellite Discovers a New Black Hole in our Galaxy
An X-ray outburst caught by NASA's Swift on Sept. 16, 2012, resulted from a flood of gas plunging toward a previously unknown black hole. Gas flowing from a sun-like star collects into a disk around the black hole. Normally, this gas would steadily spiral inward. But in this system, named Swift J1745-26, the gas collects for decades before suddenly surging inward. Credit: NASA's Goddard Space Flight Center
› Download video in high resolution from Goddard's Scientific Visualization Studio






Ground-based observatories detected infrared and radio emissions, but thick clouds of obscuring dust have prevented astronomers from catching Swift J1745-26 in visible light.

The nova peaked in hard X-rays -- energies above 10,000 electron volts, or several thousand times that of visible light -- on Sept. 18, when it reached an intensity equivalent to that of the famous Crab Nebula, a supernova remnant that serves as a calibration target for high-energy observatories and is considered one of the brightest sources beyond the solar system at these energies.

Even as it dimmed at higher energies, the nova brightened in the lower-energy, or softer, emissions detected by Swift's X-ray Telescope, a behavior typical of X-ray novae. By Wednesday, Swift J1745-26 was 30 times brighter in soft X-rays than when it was discovered and it continued to brighten.

"The pattern we're seeing is observed in X-ray novae where the central object is a black hole. Once the X-rays fade away, we hope to measure its mass and confirm its black hole status," said Boris Sbarufatti, an astrophysicist at Brera Observatory in Milan, Italy, who currently is working with other Swift team members at Penn State in University Park, Pa.


But under certain conditions, stable flow within the disk depends on the rate of matter flowing into it from the companion star. At certain rates, the disk fails to maintain a steady internal flow and instead flips between two dramatically different conditions -- a cooler, less ionized state where gas simply collects in the outer portion of the disk like water behind a dam, and a hotter, more ionized state that sends a tidal wave of gas surging toward the center.

"Each outburst clears out the inner disk, and with little or no matter falling toward the black hole, the system ceases to be a bright source of X-rays," said John Cannizzo, a Goddard astrophysicist. "Decades later, after enough gas has accumulated in the outer disk, it switches again to its hot state and sends a deluge of gas toward the black hole, resulting in a new X-ray outburst."

This phenomenon, called the thermal-viscous limit cycle, helps astronomers explain transient outbursts across a wide range of systems, from protoplanetary disks around young stars, to dwarf novae -- where the central object is a white dwarf star -- and even bright emission from supermassive black holes in the hearts of distant galaxies.

Swift, launched in November 2004, is managed by Goddard Space Flight Center. It is operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico and Orbital Sciences Corp. in Dulles, Va., with international collaborators in the United Kingdom and Italy and including contributions from Germany and Japan.

Related Links:

› Swift website
› Video on the NASA Explorer YouTube channel

Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.