Using the joint NASA and European Space Agency (ESA) Hubble Space Telescope in low-Earth orbit, an international team of astronomers has discovered a rare black hole within Omega Centauri — the largest and brightest known globular cluster in the Milky Way. Globular clusters are large collections of stars and other cosmic material that can span from 10 to 300 light-years across and have masses ranging from 1,000 to greater than 1,000,000 solar masses.
The team, led by Maximilian Häberle of the Max Planck Institute for Astronomy in Germany, used over 500 images collected by Hubble during the last two decades to detect seven rapidly moving stars in the inner regions of the globular cluster. The movement of these stars, their location and the environment surrounding them, allowed scientists to determine the location and existence of the black hole.
However, the black hole discovered within Omega Centauri is not one of the common stellar or supermassive black holes. Instead, the astronomers believe it is an intermediate-mass black hole (IMBH) — a type of black hole that has long been thought to be a “missing link” in astronomers’ understanding of black hole evolution. These black holes are extremely rare, with only a few other IMBH candidates having ever been discovered to date.
The masses of IMBHs are situated between the relatively lightweight masses of stellar black holes and the immense masses of supermassive black holes that are found at the centers of most galaxies. Scientists consider black holes to play host to the most — if not the most — extreme environments in the universe, allowing scientists to use black holes as testing grounds for the laws of physics and their understanding of how the universe works. Given how rare IMBHs are, scientists know very little about them. Fortunately, the discovery of the IMBH within Omega Centauri is allowing scientists to finally ask questions like “Does a supermassive black hole grow from an IMBH? How do IMBHs themselves form?” and “Are dense star clusters an IMBH’s favored home?”
Hubble image of Omega Centauri. (Credit: ESA/Hubble/NASA/M. Häberle)
Located approximately 17,000 light-years away, Omega Centauri has long been known as the brightest and largest globular cluster in the night sky. When observed in areas with low light pollution, it appears nearly as large as a full moon. Globular clusters can contain up to one million stars at once and are often found in the outskirts and central regions of galaxies.
However, Omega Centauri features several characteristics that distinguish it from other globular clusters. For example, Omega Centauri rotates much faster than most globular clusters, and its shape is highly flattened. What’s more, Omega Centauri is around 10 times more massive than other large globular clusters, with it being nearly as massive as a small galaxy.
Current estimates have Omega Centauri containing around 10 million stars that are all gravitationally bound to the center of the cluster. To better understand the motions of the stars within the cluster, Häberle et al. created an enormous catalog of the velocities of around 1.4 million stars using over 500 Hubble images of the cluster. Interestingly, most of the Hubble images used by the team to construct their catalog were not taken for scientific use, but rather to calibrate the telescope’s instrument. Häberle et al.’s catalog is now the largest catalog of motions for any star cluster to date and will be openly available to the public at a later date.
However, when working through their catalog, the team noticed seven stars that were seemingly out of place within Omega Centauri and moving at such incredible velocities that they should have been escaping the cluster—not staying within it.
“We discovered seven stars that should not be there. They were moving so fast that they should escape the cluster and never come back. The most likely explanation is that a very massive object is gravitationally pulling on these stars and keeping them close to the center. The only object that can be so massive is a black hole, with a mass at least 8,200 times that of our Sun,” explained Häberle.
Image showing the possible location of the IMBH within Omega Centauri. (Credit: ESA/Hubble/NASA/M. Häberle)
Several studies have been released in the last decade that suggest the presence of an IMBH within Omega Centauri. These studies proposed that a cluster of stellar-mass black holes at the center of Omega Centauri could have contributed to the mass of the IMBH. Additionally, these studies suggested that the lack of fast-moving stars above the velocity needed to escape the cluster’s gravity made the existence of an IMBH less likely.
“This discovery is the most direct evidence so far of an IMBH in Omega Centauri. This is exciting because there are only very few other black holes known with a similar mass. The black hole in Omega Centauri may be the best example of an IMBH in our cosmic neighborhood,” said co-author Nadine Neumayer of the Max Planck Institute for Astronomy, who initiated the study.
If the existence of an IMBH within Omega Centauri is confirmed, the black hole will reside closer to Earth (~17,000 light-years) than the 4.3 million solar mass supermassive black hole located at the center of the Milky Way (~26,000 light-years). Additionally, the IMBH would be the only known case of a black hole having several stars closely bound around it.
With a potential candidate IMBH within Omega Centauri, Häberle et al. now plan to characterize the IMBH and learn more about its characteristics and surrounding environment. The team currently estimates the mass of the IMBH to be around 8,200 solar masses, though its exact mass and location are still unknown. Furthermore, the team is planning to study the orbits of the seven fast-moving stars that are bound to the IMBH — a study that will require additional measurements of the velocities of the stars. Fortunately, Häberle et al. have already been granted time with the joint NASA, ESA, and Canadian Space Agency (CSA) infrared James Webb Space Telescope and plans to use Webb for their study of the seven stars. The team also has other proposals to use other observatories that are currently pending approval.
“Even after 30 years, the Hubble Space Telescope, with its imaging instruments, is still one of the best tools for high-precision astrometry in crowded stellar fields, regions where Hubble can provide added sensitivity from ESA’s Gaia mission observations. Our results showcase Hubble’s high resolution and sensitivity that are giving us exciting new scientific insights and will give a new boost to the topic of IMBHs in globular clusters,” said co-author Mattia Libralato of the National Institue for Astrophysics in Italy (INAF).
Häberle et al.’s results were published in the journal Nature on July 10.
The team’s catalog of 1,395,781 stars in Omega Centauri, named oMEGACat II, was submitted in April.
(Lead image: Image of Omega Centauri taken by ESO’s La Silla Observatory. Credit: ESO)
The post Astronomers use Hubble to discover rare intermediate-mass black hole in Omega Centauri appeared first on NASASpaceFlight.com.
Comments
Post a Comment