Because the galaxy is too far away for astronomers to employ stereoscopic vision, they instead followed the motion of stars around the center of M87, like bees around a hive. This developed a three-dimensional view of how stars are distributed within the galaxy. Credit: NASA, ESA, Joseph Olmsted (STScI), Frank Summers (STScI), Chung-Pei Ma (UC Berkeley) Mapping excellent speeds around a giant elliptical galaxy exposes its asymmetric structure.
Researchers have discovered that the M87 galaxy, formerly believed to be balanced, is really unbalanced. They identified its supermassive great void has a mass of 5.37 billion times that of the sun, which might assist them find out about the black holes spin.
Seen from Earth, the huge elliptical galaxy M87 is just a two-dimensional blob, though one that appears perfectly symmetrical and thus a preferred target of amateur astronomers.
Precise measurements by UC Berkeley astronomers revealed the motion of stars within the elliptical galaxy, revealing that it is formed more like a potato, what astronomers call a triaxial galaxy. The Virgo Cluster of galaxies, with the huge elliptical galaxy M87 at the upper. While spiral galaxies tend to be small, turn quickly, and have a well-recognized pancake shape, giant elliptical galaxies rotate gradually and have a blobby look, their 3D shape hard to discern. Like M87, the largest galaxy in the massive Virgo Cluster of galaxies, giant elliptical galaxies have grown from the merger of numerous other galaxies. The previous estimate of the mass of the supermassive black hole in M87, released in 2011, was based on a similar analysis of the dynamical motion of stars around the black hole, though that research study presumed the galaxy was axisymmetric.
Yet, a brand-new, extremely in-depth analysis of the movement of stars around its central supermassive black hole– the very first black hole to be imaged by the Event Horizon Telescope (EHT) in 2019– reveals that its not as best as it looks.
M87 is extremely unbalanced, like a russet potato. The galaxys fastest axis is about three-fourths (72.2%) the length of its long axis, while the intermediate axis is about seven-eighths (84.5%) that of the long axis.
Understanding this, University of California, Berkeley, astronomers were able to figure out the mass of the supermassive black hole at the galaxys core to a high precision, estimating it at 5.37 billion times the mass of the sun. By comparison, our own Milky Way has at its center an enormous black hole only 4 million times the mass of the sun.
They also were able to determine the rotation of the galaxy, which is a reasonably sedate 25 kilometers per second. Interestingly, it is not rotating around any of the galaxys major axes, however instead about an axis that is 40 degrees away from the long axis of its 2D image as observed by the Hubble Space Telescope.
To observers, M87 appears like an in proportion blob of stars. Meticulous measurements by UC Berkeley astronomers exposed the movement of stars within the elliptical galaxy, showing that it is shaped more like a potato, what astronomers call a triaxial galaxy. Credit: Animation by NASA, ESA, Joseph Olmsted/STScI; 3D model by Frank Summers/STScI; Science by Chung-Pei Ma/UC Berkeley
The stereo reconstruction of the M87 galaxy and the more accurate figure for the mass of the main great void could assist astrophysicists learn more about an attribute of the great void theyve had no method to determine before for any great void: its spin.
” Now that we understand the instructions of the net rotation of stars in M87 and have actually an upgraded mass of the great void, we can combine this information with the fantastic information from the EHT group to constrain the spin,” stated Chung-Pei Ma, a UC Berkeley professor of astronomy and of physics who led the research team. “This might point towards a particular instructions and series of spin for the great void, which would be exceptional. We are dealing with this.”
Further analyses to figure out the true shape of giant elliptical galaxies– the galaxies with the largest black holes at their cores– will assist astronomers comprehend better how large galaxies and big great voids form and might assist astronomers much better analyze gravitational wave signals. Ma leads a long-term study of supermassive black holes that is called MASSIVE.
The results were recently published in The Astrophysical Journal Letters (ApJ Letters).
The Virgo Cluster of galaxies, with the giant elliptical galaxy M87 at the upper. In spite of its seeming symmetry, a UC Berkeley research study reveals that M87s 3D shape is extremely asymmetric. This decision helps improve quotes of the mass of the supermassive black hole at the galaxys. Credit: Fernando Pena
Figuring out a galaxys 3D shape
While spiral galaxies tend to be little, rotate quickly, and have a well-recognized pancake shape, giant elliptical galaxies turn slowly and have a blobby appearance, their 3D shape challenging to recognize. Like M87, the largest galaxy in the huge Virgo Cluster of galaxies, huge elliptical galaxies have grown from the merger of many other galaxies. Thats likely the reason M87s central great void is so large– it absorbed the central black holes of all the galaxies it swallowed. In all, the galaxy includes about 100 billion stars, 10 times bigger than the Milky Way.
Ma, UC Berkeley graduate student and lead author Emily Liepold, and Jonelle Walsh at Texas A&M University in College Station were able to determine the 3D shape of M87 thanks to a relatively brand-new precision instrument installed on the Keck II Telescope, among the twin 10-meter Keck telescopes atop Mauna Kea, a volcano in Hawaii. Called the Keck Cosmic Web Imager (KCWI), the essential field spectrometer enabled Ma and her team to measure the spectra of stars in the center of the galaxy.
They pointed the telescope at 62 nearby places in the galaxy, entirely covering a region about 70,000 light-years across, and recorded the spectra of stars within that region. The observations span the central area– about 3,000 light-years across– where gravity is mainly controlled by the supermassive black hole, along with the external part dominated by dark matter. Though the telescope can not fix specific stars– M87 lies about 53 million light-years from Earth– the spectra can expose the series of speeds within each pixel of each image, adequate information to calculate the gravitational mass theyre orbiting.
” Its sort of like taking a look at a swarm of 100 billion bees that are going around in their own delighted orbits,” stated Ma, the Judy Chandler Webb Professor in the Physical Sciences. “Though we are looking at them from a distance and cant determine individual bees, we are getting very comprehensive information about their collective speeds. Its actually the excellent sensitivity of this spectrograph that enabled us to map out M87 so thoroughly.”
This is the very first time KCWI has been used to reconstruct the geometry of a remote galaxy, and M87 is among only a handful of huge elliptical galaxies whose 3D structure has been identified. Mas team had actually previously determined the 3D structure of 2 other giant elliptical galaxies, NGC 1453 and NGC 2693, both harboring smaller sized black holes than M87.
The scientists took the data obtained during four nights of Keck observations between 2020 and 2022, together with earlier photometric data for M87 from NASAs Hubble Space Telescope, and compared them to computer design predictions of how stars move the center of a triaxial galaxy. The very best fit to the data– axial ratios of 1 to 0.84 to 0.72– then permitted them to compute the black hole mass.
” The Keck information are so good that we can determine the intrinsic shape of M87 along with the black hole at the very same time,” Ma stated. “We made the very first measurement of the actual 3D shape of the galaxy. And given that we allowed the swarm of bees to have a more general shape than just a sphere or disk, we have a more robust dynamical measurement of the mass of the main great void that is governing the bees orbiting velocities.”
The authors devoted their manuscript to the late astronomer Wallace “Wal” Sargent, who first recommended that a supermassive black hole lurked at the center of M87 and computed its mass to be about 5 billion solar masses.
” His number is a twiddle with our mistake bars, which is extremely intriguing to see after years of work,” stated Ma, who credits Sargent with being a mentor when she was a postdoctoral fellow at the California Institute of Technology.
The previous price quote of the mass of the supermassive black hole in M87, released in 2011, was based on a similar analysis of the dynamical motion of stars around the great void, though that research study assumed the galaxy was axisymmetric. The number, 6.14 billion solar masses, is within mistake bars of the brand-new, more accurate quote. When imaging the great void four years earlier, the EHT scientists estimated the great void mass to be 6.5 billion solar masses, 21% higher than the new number.
Interestingly, the dark matter within the volume of the galaxy they analyzed is much higher than that of the great void– about 388 billion solar masses, or 67% of the whole mass of M87. The identity of dark matter is still a secret, it makes up about 85% of the mass of the universe.
For more on this research, see M87 Galaxys True 3D Shape Revealed.
Recommendation: “Keck Integral-field Spectroscopy of M87 Reveals an Intrinsically Triaxial Galaxy and a Revised Black Hole Mass” by Emily R. Liepold, Chung-Pei Ma and Jonelle L. Walsh, 15 March 2023, Astrophysical Journal Letters.DOI: 10.3847/ 2041-8213/ acbbcf.
Jonelle Walsh is with the George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M. The work was funded by the National Science Foundation (AST-1817100, AST-2206307), the Heising-Simons Foundation and the Miller Institute for Basic Research in Science.