The Astrophysical Journal Letters announces a discovery that could upend our perception of supermassive black holes. Astronomers have shown that a small X-ray point cataloged by the Chandra Space Telescope exactly matches one of the little red dots from James Webb data. Thus, its true nature has been revealed.
The "little red dots" are among the most intriguing objects discovered by James Webb. Compact and very red, they existed over 11 billion years ago, in the early days of the cosmos. Their exact nature remained unclear, but a link with an X-ray observation has now provided a decisive clue.
A window into the heart of a little red dot, revealing the supermassive black hole it harbors.
Credit: NASA/CXC/SAO/M. Weiss; adapted by K. Arcand and J. Major
This X-ray point, named 3DHST-AEGIS-12014, coincides exactly with a little red dot observed by Webb. The energy detected by Chandra is similar to that of quasars, galaxies whose central black hole is particularly active. This indicates that the little red dots could be immense gas clouds harboring a growing black hole.
The little red dots are very compact objects, only a few hundred light-years in diameter. Their red color reflects a relatively low temperature, between 1700 and 3700 degrees Celsius (about 3100 to 6700 degrees Fahrenheit), cooler than our Sun.
These objects would thus resemble a giant red star, but whose heart would be a supermassive black hole.
One of the main questions in astrophysics is how giant black holes are born. Two scenarios compete: bottom-up formation, by merging massive stars, or top-down formation, by direct collapse of a gas cloud. The little red dots strongly lean toward the second hypothesis, that of a gas cloud contracting to give birth to a black hole.
The X-ray point observed by Chandra stands out from other little red dots because it emits X-rays, which is unprecedented for this type of object. Astronomers think it is a transitional object: the black hole, feeding on the gas cloud, would have created "windows" that allow X-rays to escape. This is the first direct observation of this process.
This discovery could help link the formation of supermassive black holes to that of the galaxies that surround them. The little red dots would then be a missing piece of the cosmic puzzle, helping us understand how our own Milky Way has evolved since its beginnings.