Evidence for two pairs of supermassive black holes in dwarf galaxies on collision courses has been found with Chandra. The two pairs are shown in X-rays from Chandra and optical light from the Canada-France-Hawaii telescope. The merger on the left is in a late stage and was given the single name of Mirabilis. The other merger is in the early stages and the two dwarf galaxies are named Elstir (bottom) and Vinteuil (top). Astronomers think that dwarf galaxies – those about 20 times less massive than the Milky Way – grow through mergers with others. This is an important process for galaxy growth in the early Universe and this discovery provides examples for scientists to study in greater detail. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
Astronomers discovered the first evidence of giant black holes in colliding dwarf galaxies, offering important insights into early universe galaxy formation and black holeA black hole is a place in space where the gravitational field is so strong that not even light can escape it. Astronomers classify black holes into three categories by size: miniature, stellar, and supermassive black holes. Miniature black holes could have a mass smaller than our Sun and supermassive black holes could have a mass equivalent to billions of our Sun.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>black hole growth. The findings were made using NASAEstablished in 1958, the National Aeronautics and Space Administration (NASA) is an independent agency of the United States Federal Government that succeeded the National Advisory Committee for Aeronautics (NACA). It is responsible for the civilian space program, as well as aeronautics and aerospace research. Its vision is "To discover and expand knowledge for the benefit of humanity." Its core values are "safety, integrity, teamwork, excellence, and inclusion." NASA conducts research, develops technology and launches missions to explore and study Earth, the solar system, and the universe beyond. It also works to advance the state of knowledge in a wide range of scientific fields, including Earth and space science, planetary science, astrophysics, and heliophysics, and it collaborates with private companies and international partners to achieve its goals.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>NASA’s Chandra X-ray Observatory, WISE, and CFHT data.
Astronomers have discovered the first evidence of giant black holes in dwarf galaxies on a collision course. This result from NASA’s Chandra X-ray Observatory has important ramifications for understanding how the first wave of black holes and galaxies grew in the early universe.
Collisions between the pairs of dwarf galaxies identified in a new study have pulled gas toward the giant black holes they each contain, causing the black holes to grow. Eventually, the likely collision of the black holes will cause them to merge into much larger black holes. The pairs of galaxies will also merge into one.
Scientists think the universe was awash with small galaxies, known as “dwarf galaxies,” several hundred million years after the big bang. Most merged with others in the crowded, smaller volume of the early universe, setting in motion the building of larger and larger galaxies now seen around the nearby universe.
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Dwarf galaxies by definition contain stars with a total mass less than about 3 billion times that of the Sun, compared to a total mass of about 60 billion Suns estimated for the Milky WayThe Milky Way is the galaxy that contains our Solar System and is part of the Local Group of galaxies. It is a barred spiral galaxy that contains an estimated 100-400 billion stars and has a diameter between 150,000 and 200,000 light-years. The name "Milky Way" comes from the appearance of the galaxy from Earth as a faint band of light that stretches across the night sky, resembling spilled milk.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Milky Way.
The earliest dwarf galaxies are impossible to observe with current technology because they are extraordinarily faint at their large distances. Astronomers have been able to observe two in the process of merging at much closer distances to Earth, but without signs of black holes in both galaxies.
“Astronomers have found many examples of black holes on collision courses in large galaxies that are relatively close by,” said Marko Micic of the University of Alabama at Tuscaloosa, who led the study. “But searches for them in dwarf galaxies are much more challenging and until now had failed.”
X-ray and optical composite of Mirabilis. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
The new study overcame these challenges by implementing a systematic survey of deep Chandra X-ray observations and comparing them with infrared data from NASA’s Wide Infrared Survey Explorer (WISE) and optical data from the Canada-France-Hawaii Telescope (CFHT).
Chandra was particularly valuable for this study because material surrounding black holes can be heated up to millions of degrees, producing large amounts of X-rays. The team searched for pairs of bright X-ray sources in colliding dwarf galaxies as evidence of two black holes, and discovered two examples.
“We’ve identified the first two different pairs of black holes in colliding dwarf galaxies,” said co-author Olivia Holmes, also of the University of Alabama at Tuscaloosa. “Using these systems as analogs for ones in the early universe, we can drill down into questions about the first galaxies, their black holes, and star formation the collisions caused.”
X-ray and optical composite of Elstir & Vinteuil. Credit: X-ray: NASA/CXC/Univ. of Alabama/M. Micic et al.; Optical: International Gemini Observatory/NOIRLab/NSF/AURA
One pair is in the galaxy cluster Abell 133 located 760 million light-years from Earth. The other is in the Abell 1758S galaxy cluster, which is about 3.2 billion light-years away. Both pairs show structures that are characteristic signs of galaxy collisions.
The pair in Abell 133 appears to be in the late stages of a merger between the two dwarf galaxies, and shows a long tail caused by tidal effects from the collision. The authors of the new study have nicknamed it “Mirabilis” after an endangered speciesA species is a group of living organisms that share a set of common characteristics and are able to breed and produce fertile offspring. The concept of a species is important in biology as it is used to classify and organize the diversity of life. There are different ways to define a species, but the most widely accepted one is the biological species concept, which defines a species as a group of organisms that can interbreed and produce viable offspring in nature. This definition is widely used in evolutionary biology and ecology to identify and classify living organisms.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>species of hummingbird known for their exceptionally long tails. Only one name was chosen because the merger of two galaxies into one is almost complete.
In Abell 1758S, the researchers nicknamed the merging dwarf galaxies “Elstir” and “Vinteuil,” after fictional artists from Marcel Proust’s “In Search of Lost Time.” The researchers think these two have been caught in the early stages of a merger, causing a bridge of stars and gas to connect the two colliding galaxies.
The details of merging black holes and dwarf galaxies may provide insight to our Milky Way’s own past. Scientists think nearly all galaxies began as dwarf or other types of small galaxies and grew over billions of years through mergers.
“Most of the dwarf galaxies and black holes in the early universe are likely to have grown much larger by now, thanks to repeated mergers,” said co-author Brenna Wells, also of the University of Alabama at Tuscaloosa. “In some ways, dwarf galaxies are our galactic ancestors, which have evolved over billions of years to produce large galaxies like our own Milky Way.”
“Follow-up observations of these two systems will allow us to study processes that are crucial for understanding galaxies and their black holes as infants,” said co-author Jimmy Irwin, also from the University of Alabama at Tuscaloosa.
A paper describing these results was published in the latest issue of The Astrophysical JournalThe Astrophysical Journal (ApJ) is a peer-reviewed scientific journal that focuses on the publication of original research on all aspects of astronomy and astrophysics. It is one of the most prestigious journals in the field, and is published by the American Astronomical Society (AAS). The journal publishes articles on a wide range of topics, including the structure, dynamics, and evolution of the universe; the properties of stars, planets, and galaxies; and the nature of dark matter, dark energy, and the early universe.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>Astrophysical Journal.
For more on this discovery, see NASA’s Chandra Discovers Supermassive Black Holes on Collision Course.
Reference: “Two Candidates for Dual AGN in Dwarf-Dwarf Galaxy Mergers” by Marko Mićić, Olivia J. Holmes, Brenna N. Wells and Jimmy A. Irwin, 22 February 2023, The Astrophysical Journal.
DOI: 10.3847/1538-4357/aca1bb
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.
Source: SciTechDaily
