Astronomers may have witnessed a galaxy’s black hole delivery system in action. A new study using data from NASA’s Chandra X-ray Observatory and Hubble Space Telescope outlines how a large black hole may have been delivered to the spiral galaxy NGC 4424 by another, smaller galaxy.
NGC 4424 is located about 54 million light-years from Earth in the Virgo galaxy cluster. The main panel shows a wide-field view, about 45,000 light-years wide, of this galaxy in optical light from Hubble. The center of this galaxy is expected to host a large black hole estimated to contain a mass between 60,000 and 100,000 Suns.
Astronomers examining data from NASA’s Chandra X-ray Observatory found an elongated object, which they determined is a cluster of stars. They refer to this object as “Nikhuli,” a name relating to the Tulini festive period of celebrating and wishing for a rich harvest. This name is taken from the Sumi language from the Indian state of Nagaland. The Chandra data shows a point source of X-rays.
The researchers determined Nikhuli is likely the center of a small galaxy that has had most of its stars stripped away as it collides with the larger galaxy NGC 4424. Nikhuli has also been stretched out by gravitational forces as it falls towards the center of NGC 4424, giving it an elongated shape. Currently, Nikhuli is about 1,300 light-years from the center of NGC 4424, or about 20 times closer than the Earth is to the Milky Way’s giant black hole.
After considering other possibilities, the researchers determined that these results imply that Nikhuli is likely acting as a delivery system for NGC 4424’s supply of black holes, in this case bringing along a massive one. If the center of NGC 4424 contains a massive black hole, Nikhuli’s massive black hole should end up orbiting it. The separation of the pair should then shrink until gravitational waves are produced and the two massive black holes merge with each other.
Revised: March 24, 2023