The Center for Astrophysics | Harvard & Smithsonian
The Center for Astrophysics | Harvard & Smithsonian
Support Our Science

A Black Hole in a Low Mass X-Ray Binary

Share this Page
Research Topics
Science Fields
A Black Hole in a Low Mass X-Ray Binary

An optical image of the globular cluster 47 Tuc taken by Hubble. There are numerous known low-mass X-ray binary stars (LMXBs) in this and other globular clusters. Astronomers report finding what might be the the first LMXB whose compact object is a black hole rather than a neutron star.

NASA/Hubble Space Telescope

A globular cluster is a roughly spherical ensemble of stars (as many as several million) that are gravitationally bound together, and typically located in the outer regions of galaxies. Low mass X-ray binary stars (LMXBs) are systems in which one star is compact (a neutron star or black hole) and is accreting matter from a companion star. Astronomers have long noticed that there are fractionally many more LMXBs in globular clusters than elsewhere in the galaxy, an overabundance that is usually attributed to the high stellar density in globular clusters. But this calls attention to another unusual feature of the LMXBs in globulars. In the galactic field, most LXMBs are formed from binary stars as they age and evolve, but in globular clusters it has been shown that most LMXBs form when compact objects encounter and then capture another star. There are many neutron stars in clusters, but black holes that form in these dense stellar environments are expected either to sink down to the center of the cluster or else to be gravitationally ejected from the cluster after they are formed. Indeed, all of the LMXBs seen in globular clusters are of the type with a neutron star.

CfA astronomer Javier Garcia was a member of a team studying LMXBs in the 47 Tuc globular cluster. They discovered one, called X9, that appears to contain a black hole, and if the interpretation is correct X9 would be the first such case in our Galaxy. The team used simultaneous observations of the source with Chandra, NuSTAR, and the Australia Compact Array, plus archival datasets, to find a twenty-eight minute modulation of the signal from X9, such as would be produced by a black hole of about one solar mass orbited by a white dwarf star of about 0.02 solar-masses. The source has some other unusual characteristics, including a precession period of 6.8 days, and a relatively high rate of mass transfer for LMXBs, about seven-millionths of an Earth-mass per year.

"The Ultracompact Nature of the Black Hole Candidate X-Ray Binary 47 Tuc X9," Arash Bahramian,Craig O. Heinke, Vlad Tudor, James C. A. Miller-Jones, Slavko Bogdanov, Thomas J. Maccarone, Christian Knigge, Gregory R. Sivakoff, Laura Chomiuk, Jay Strader, Javier A. Garcia and Timothy Kallman, MNRAS 467, 2199, 2017.

Related News

Projects

AstroAI

Atomic and Molecular Physics, High Energy Astrophysics, Optical and Infrared Astronomy, Radio and Geoastronomy, Solar, Stellar, and Planetary Sciences, Theoretical Astrophysics, Harvard University Department of Astronomy, Science Education Department, Central Engineering, Director's Office, Chandra X-ray Center, Institute for Theoretical Atomic Molecular and Optical Physics, Institute for Theory and Computation
AstroAI is a institute dedicated to the development of artificial intelligence to enable next generation astrophysics at the Center for Astrophysics | Harvard & Smithsonian. Learn More
1

DASCH (Digital Access to a Sky Century @ Harvard)

High Energy Astrophysics
The Harvard Astronomical Glass Plate Collection is an archive of roughly 500,000 images of the sky preserved on glass photographic plates, the way professional astronomers often captured images in the era before the dominance of digital technology. These plates are more than historical curiosities: they provide over a century’s worth of data that can be used by contemporary astronomers to trace how objects in the night sky change over periods from years to decades.

For that reason, the DASCH (Digital Access to a Sky Century @ Harvard) team are working to digitize the plates for digital storage and analysis. The process can also lead to new discoveries in old images, particularly of events that change over time, such as variable stars, novas, or black hole flares. 
2

GMACS

Optical and Infrared Astronomy, Central Engineering
GMACS - Moderate Dispersion Optical Spectrograph for the Giant Magellan Telescope is a powerful optical spectrograph that will unlock the power of the Giant Magellan Telescope for research ranging from the formation of stars and planets to cosmology.

For Scientists
3

Sensing the Dynamic Universe

High Energy Astrophysics, Optical and Infrared Astronomy, Solar, Stellar, and Planetary Sciences, Science Education Department
The Sensing the Dynamic Universe (SDU) project creates sonified videos exploring the multitude of celestial variables such as stars, supernovae, quasars, gamma ray bursts and more. We sonify lightcurves and spectra, making the astrophysics of variables and transients accessible to the general public, with particular attention to accessibility for those with visual and/or neurological differences.

SDU Website
4

ChaMP (Chandra Multiwavelength Project) and ChaMPlane (Chandra Multiwavelength Plane) Survey

High Energy Astrophysics
NASA’s Chandra X-ray Observatory is a groundbreaking space telescope, with abilities beyond anything that came before it. The Chandra Multiwavelength Project (ChaMP) and Chandra Multiwavelength Plane (ChaMPlane) Survey exploit those abilities to catalog the variety of X-ray sources within archival Chandra data, with follow-up using other telescopes in other parts of the spectrum of light. The surveys identified previously unknown galaxy clusters, quasars, neutron star binary systems, and other significant astronomical sources both in the plane of the Milky Way — ChamPLane — and beyond the galaxy — ChaMP. ChaMP and ChaMPlane are led by astronomers at the Center for Astrophysics | Harvard & Smithsonian, in collaboration with researchers at a number of other institutions in the United States and around the world.
5