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XBONGS: Astronomers Dig Out Buried Black Holes With NASA's Chandra
XBONGS

  • Hundreds of supermassive black holes have been identified in a new survey using NASA’s Chandra X-ray Observatory.

  • The key to this finding was comparing objects in the Chandra Source Catalog to data from Sloan Digitized Sky Survey.

  • Researchers focused on a class of objects known as “XBONGs” (X-ray bright, optically normal galaxies).

  • This result adds to the ongoing tally of black holes and helps explain long-standing questions about XBONGs.

This panel of images represents a survey that used data from NASA’s Chandra X-ray Observatory to uncover hundreds of previously “hidden” black holes. This result helps astronomers conduct a more accurate census of supermassive black holes that exist in the centers of most large galaxies, as reported in our latest press release.

This graphic shows two of the galaxies from the new study, with Chandra X-ray data in purple and optical data from the Sloan Digital Sky Survey (SDSS) in red, green and blue. These black holes were found in galaxies that are dim in optical light, but bright in X-rays. Astronomers have dubbed these “XBONGs” (for X-ray bright, optically normal galaxies). While scientists have been aware of XBONGs for several decades, an explanation for their unusual properties has been unclear.

Two, 2-panel images showing an X-ray image on the left-hand side and an optical image on the right-hand side. The optical images have a pink circle around the object that shown in the X-ray image on the left.
Labeled X-ray and optical images of SDSS J011522.18+001518.5 and SDSS J155627.74+241758.9. (Credit: X-ray: NASA/CXC/SAO/D. Kim et al.; Optical/IR: Legacy Surveys/D. Lang (Perimeter Institute))

The team made this advance by comparing data from the Chandra Source Catalog — an online public repository of data from the mission’s first 15 years — with those from SDSS. Chandra’s sharp images, matching the quality of those from SDSS, and the large amount of data in the Chandra Source Catalog made it possible for the researchers to detect 817 XBONG candidates — more than ten times the number known before Chandra was in operation. Further study revealed that about half of these XBONGs represent a population of previously-hidden black holes.

The black holes in this study belong to the “supermassive” category, meaning they contain millions or even billions of times the mass of the Sun. Their presence can be revealed by radiation from material they are actively pulling in as they grow, but some of these black holes are enshrouded by material that blocks most light from escaping. X-rays are particularly useful to search for rapidly growing black holes because material swirling around them is superheated to millions of degrees that glow strongly in X-ray wavelengths. A thick cocoon of gas and dust surrounding a black hole will block most or all the light at optical wavelengths. X-rays, however, pass through the cocoon much more easily to be detected by Chandra.

The X-ray sources in this new study are so bright that almost all of them must be from material surrounding rapidly growing supermassive black holes. Data from NASA's Wide-Field Infrared Survey Explorer provides additional evidence that about half of the XBONGs are buried, growing supermassive black holes. These black holes range in distances between 550 million and 7.8 billion light-years from Earth.

A 2-panel image showing an X-ray image on the left-hand side and an optical image on the right-hand side. The optical image has a pink circle around the object that shown in the X-ray image.
Labeled X-ray and optical images of SDSS J102155.55+344103.2. (Credit: X-ray: NASA/CXC/SAO/D. Kim et al.; Optical/IR: Legacy Surveys/D. Lang (Perimeter Institute))

These results were presented by Dong-Woo Kim of the Center for Astrophysics | Harvard & Smithsonian at the 241st meeting of the American Astronomical Society in Seattle, WA. Other members of the research team included Amanda Malnati, an undergraduate at Smith College, and Alyssa Cassidy, a graduate student at the University of British Columbia.

NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.

 

Fast Facts for SDSS J011522.18+001518.5:
Credit  X-ray: NASA/CXC/SAO/D. Kim et al.; Optical/IR: Legacy Surveys/D. Lang (Perimeter Institute)
Release Date  January 11, 2023
Scale  X-ray image is about (2.1 million light-years) across.
Category  Normal Galaxies & Starburst Galaxies, Black Holes
Coordinates (J2000)  RA 1h 15m 22.2s | Dec +00° 15´ 18.6"
Constellation  Cetus
Observation Date  Nov 1, 2002
Observation Time  hours 27 minutes
Obs. ID  3204
Instrument  ACIS
References Kim, D. et al., AAS Meeting #241, 2023, id, 408.03.
Color Code  X-ray: purple; Optical/IR: red, green, blue
Optical
X-ray
Distance Estimate  About 4.2 billion light-years (z=0.3902)
distance arrow

 

Fast Facts for SDSS J155627.74+241758.9:
Credit  X-ray: NASA/CXC/SAO/D. Kim et al.; Optical/IR: Legacy Surveys/D. Lang (Perimeter Institute)
Release Date  January 11, 2023
Scale  X-ray image is about (1.3 million light-years) across.
Category  Normal Galaxies & Starburst Galaxies, Black Holes
Coordinates (J2000)  RA 15h 56m 27.7s | Dec +24° 17´ 59.0"
Constellation  Serpens
Observation Date  Apr 12, 2003
Observation Time  hours 34 minutes
Obs. ID  3984
Instrument  ACIS
References Kim, D. et al., AAS Meeting #241, 2023, id, 408.03.
Color Code  X-ray: purple; Optical/IR: red, green, blue
Optical
X-ray
Distance Estimate  About 1.5 billion light-years (z=0.1182)
distance arrow

 

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