Scientists are questioning if there is any upper size limit to black holes either within or beyond the observable universe. In December of 2019, astronomers announced the discovery of one of the most perfect macroscopic objects, the largest hard-disk in the cosmos –the biggest black hole ever measured in the nearby universe at the center of an elliptical galaxy in galaxy cluster Abel 85 that’s 40 billion times the sun’s mass, or roughly the size of our solar system, harboring two-thirds the mass of the 100-billion stars in the Milky Way.
“Only Elements in Their Construction are Our Concepts of Space and Time”
Noble-Prize laureate Subrahmanyan Chandrasekhar, for whom NASA’s Chandra X-Ray Observatory was named, described black holes the only elements in their construction are our concepts of space and time,” which has inspired astrophysicists to question how big these paradoxical objects, these “Gates of Hell” that have no memory, yet are said to contain the earliest memories of the universe, might become?
Astronomers at the Max Planck Institute for Extraterrestrial Physics and at the University Observatory discovered the monster by evaluating photometric data as well as new spectral observations with the Very Large Telescope. The galaxy is Holm 15A, a huge elliptical galaxy at the center of a cluster of galaxies called Abell 85, which consists of more than 500 individual galaxies, at a distance of 700 million lightyears from Earth, twice the distance for previous direct black hole mass measurements.
“There are only a few dozen direct mass measurements of supermassive black holes, and never before has it been attempted at such a distance,” explains MPE scientist Jens Thomas, who led the study. “But we already had some idea of the size of the black hole in this particular galaxy, so we tried it.” The team captured a snapshot of Holm 15A’s stars in orbit around the galaxy’s central black hole and created a model to help them calculate the black hole’s mass.
“Just imagining a black hole that is so huge is cool,” said Thomas, an astronomer at the Max Planck Institute for Extraterrestrial Physics and one of the study’s authors.
In the far distant universe some 10 billion light years away lurks the very luminous quasar TON 618 – an even more massive than Holm 15A estimated have a mass of 66 billion times that of our sun. Gargantuan black holes like TON 618 may shed light on the nature of a significant fraction of the mysterious dark matter. These “stupendously large black holes” (SLABs) in galactic nuclei, exist in theory and may have been seeded by primordial black holes, suggests Florian Kuhnel who holds the Chair on Cosmology at the Arnold Sommerfeld Center for Theoretical Physics. This largest known black hole in the observable universe leads to conjectures that even larger exist either within or beyond the observable universe, and to question if there is any upper limit to their sizes.
In crowded like galaxy clusters, these huge elliptical galaxies like Holm 15A can collide and merge again to form an even larger elliptical galaxy. Their central black holes combine as well and make larger black holes, galactic monsters which kick huge swaths of nearby stars out to the edges of the newly formed galaxy leaving its faint center barren, or “cored.”
The authors of the study found that Holm 15A, formed from yet another merger of two already-huge cored elliptical galaxies that wprobably formed from the combination of eight smaller spiral galaxies over billions of years. Pairs of spiral galaxies form elliptical galaxies, pairs of those ellipticals form cored elliptical galaxies, and a pair of cored galaxies formed Holm 15A. This series of mergers also created the black hole in its center, a monster about as big as our solar system but with the mass of 40 billion suns.
Holm 15A is similar to elliptical galaxy M87, the largest, most massive galaxy in the nearby universe, thought to have been formed by the merging of 100 or so smaller galaxies. New observations July 2018 with ESO’s Very Large Telescope revealed that the giant elliptical galaxy M87 swallowed an entire medium-sized galaxy over the last billion years. The Event Horizon Telescope (EHT) team theorized that the M87 black hole grew to its massive size by merging with several other black holes.
.“A medium-sized galaxy fell through the center of M87, and as a consequence of the enormous gravitational tidal forces, its stars are now scattered over a region that is 100 times larger than the original galaxy!” said Ortwin Gerhard, head of the dynamics group at the Max Planck Institute for Extraterrestrial Physics about the monster elliptical galaxy that harbors the now iconic black hole the size of our solar system imaged for the first time ever by the Event Horizon Telescope (EHT) on April 10, 2019.
Image credits: Shutterstock license, top of page. Abel 85 composite image, X-RAY (NASA/CXC/SAO/A.VIKHLININ ET AL.); OPTICAL (SDSS)