Black Hole Found Hiding In Star Cluster Outside Our Galaxy (Cosmology)

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered a small black hole outside the Milky Way by looking at how it influences the motion of a star in its close vicinity. This is the first time this detection method has been used to reveal the presence of a black hole outside of our galaxy. The method could be key to unveiling hidden black holes in the Milky Way and nearby galaxies, and to help shed light on how these mysterious objects form and evolve.

The newly found black hole was spotted lurking in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a neighbour galaxy of the Milky Way.

Similar to Sherlock Holmes tracking down a criminal gang from their missteps, we are looking at every single star in this cluster with a magnifying glass in one hand trying to find some evidence for the presence of black holes but without seeing them directly,” says Sara Saracino from the Astrophysics Research Institute of Liverpool John Moores University in the UK, who led the research now accepted for publication in Monthly Notices of the Royal Astronomical Society. “The result shown here represents just one of the wanted criminals, but when you have found one, you are well on your way to discovering many others, in different clusters.

This first “criminal” tracked down by the team turned out to be roughly 11 times as massive as our Sun. The smoking gun that put the astronomers on the trail of this black hole was its gravitational influence on the five-solar-mass star orbiting it.

Astronomers have previously spotted such small, “stellar-mass” black holes in other galaxies by picking up the X-ray glow emitted as they swallow matter, or from the gravitational waves generated as black holes collide with one another or with neutron stars.

However, most stellar-mass black holes don’t give away their presence through X-rays or gravitational waves. “The vast majority can only be unveiled dynamically,” says Stefan Dreizler, a team member based at the University of Göttingen in Germany. “When they form a system with a star, they will affect its motion in a subtle but detectable way, so we can find them with sophisticated instruments.

This dynamical method used by Saracino and her team could allow astronomers to find many more black holes and help unlock their mysteries. “Every single detection we make will be important for our future understanding of stellar clusters and the black holes in them,” says study co-author Mark Gieles from the University of Barcelona, Spain.

The detection in NGC 1850 marks the first time a black hole has been found in a young cluster of stars (the cluster is only around 100 million years old, a blink of an eye on astronomical scales). Using their dynamical method in similar star clusters could unveil even more young black holes and shed new light on how they evolve. By comparing them with larger, more mature black holes in older clusters, astronomers would be able to understand how these objects grow by feeding on stars or merging with other black holes. Furthermore, charting the demographics of black holes in star clusters improves our understanding of the origin of gravitational wave sources.

To carry out their search, the team used data collected over two years with the Multi Unit Spectroscopic Explorer (MUSE) mounted at ESO’s VLT, located in the Chilean Atacama Desert. “MUSE allowed us to observe very crowded areas, like the innermost regions of stellar clusters, analysing the light of every single star in the vicinity. The net result is information about thousands of stars in one shot, at least 10 times more than with any other instrument,” says co-author Sebastian Kamann, a long-time MUSE expert based at Liverpool’s Astrophysics Research Institute. This allowed the team to spot the odd star out whose peculiar motion signalled the presence of the black hole. Data from the University of Warsaw’s Optical Gravitational Lensing Experiment and from the NASA/ESA Hubble Space Telescope enabled them to measure the mass of the black hole and confirm their findings.

ESO’s Extremely Large Telescope in Chile, set to start operating later this decade, will allow astronomers to find even more hidden black holes. “The ELT will definitely revolutionise this field,” says Saracino. “It will allow us to observe stars considerably fainter in the same field of view, as well as to look for black holes in globular clusters located at much greater distances.”

More information

This research was presented in a paper to appear in Monthly Notices of the Royal Astronomical Society (

The team is composed of S. Saracino (Astrophysics Research Institute, Liverpool John Moores University, UK [LJMU]), S. Kamann (LJMU), M. G. Guarcello (Osservatorio Astronomico di Palermo, Palermo, Italy), C. Usher (Department of Astronomy, Oskar Klein Centre, Stockholm University, Stockholm, Sweden), N. Bastian (Donostia International Physics Center, Donostia-San Sebastián, Spain, Basque Foundation for Science, Bilbao, Spain & LJMU), I. Cabrera-Ziri (Astronomisches Rechen-Institut, Zentrum für Astronomie der Universität Heidelberg, Heidelberg, Germany), M. Gieles (ICREA, Barcelona, Spain and Institut de Ciències del Cosmos, Universitat de Barcelona, Barcelona, Spain), S. Dreizler (Institute for Astrophysics, University of Göttingen, Göttingen, Germany [GAUG]), G. S. Da Costa (Research School of Astronomy and Astrophysics, Australian National University, Canberra, Australia), T.-O. Husser (GAUG) and V. Hénault-Brunet (Department of Astronomy and Physics, Saint Mary’s University, Halifax, Canada).

Featured image: This artist’s impression shows a compact black hole 11 times as massive as the Sun and the five-solar-mass star orbiting it. The two objects are located in NGC 1850, a cluster of thousands of stars roughly 160 000 light-years away in the Large Magellanic Cloud, a Milky Way neighbour. The distortion of the star’s shape is due to the strong gravitational force exerted by the black hole. Not only does the black hole’s gravitational force distort the shape of the star, but it also influences its orbit. By looking at these subtle orbital effects, a team of astronomers were able to infer the presence of the black hole, making it the first small black hole outside of our galaxy to be found this way. For this discovery, the team used the Multi Unit Spectroscopic Explorer (MUSE) instrument at ESO’s Very Large Telescope in Chile. Credit: ESO/M. Kornmesser

Provided by ESO

Near-Earth Asteroid Might be a Lost Fragment of the Moon (Planetary Science)

A team of UArizona-led researchers think that the near-Earth asteroid Kamo`oalewa might actually be a miniature moon.

A near-Earth asteroid named Kamo`oalewa could be a fragment of our moon, according to a paper published today in Communications Earth and Environment by a team of astronomers led by the University of Arizona.

Kamo`oalewa is a quasi-satellite – a subcategory of near-Earth asteroids that orbit the sun but remain relatively close to Earth. Little is known about these objects because they are faint and difficult to observe. Kamo`oalewa was discovered by the PanSTARRS telescope in Hawaii in 2016, and the name – found in a Hawaiian creation chant – alludes to an offspring that travels on its own. The asteroid is roughly the size of a Ferris wheel – between 150 and 190 feet in diameter – and gets as close as about 9 million miles from Earth.

Due to its orbit, Kamo`oalewa can only be observed from Earth for a few weeks every April. Its relatively small size means that it can only be seen with one of the largest telescopes on Earth. Using the UArizona-managed Large Binocular Telescope on Mount Graham in southern Arizona, a team of astronomers led by UArizona planetary sciences graduate student Ben Sharkey found that Kamo`oalewa’s pattern of reflected light, called a spectrum, matches lunar rocks from NASA’s Apollo missions, suggesting it originated from the moon.

Researchers aren’t yet be sure how the asteroid may have broken loose from the moon. That’s partly because there are no other known asteroids with lunar origins.

“I looked through every near-Earth asteroid spectrum we had access to, and nothing matched,” said Sharkey, the paper’s lead author.

A debate over Kamo`oalewa’s origins between Sharkey and his adviser, UArizona associate professor of lunar and planetary sciences Vishnu Reddy, led to another three years of hunting for a plausible explanation.

“We doubted ourselves to death,” said Reddy, a co-author who started the project in 2016. After missing the chance to observe the asteroid in April 2020 due to a COVID-19 shutdown of the Large Binocular Telescope, the team found the final piece of the puzzle in 2021.

“This spring, we got much needed follow-up observations and went, ‘Wow it is real,'” Sharkey said. “It’s easier to explain with the moon than other ideas.”

Kamo`oalewa’s orbit is another clue to its lunar origins. Its orbit is similar to the Earth’s, but with the slightest tilt. Its orbit is also not typical of near-Earth asteroids, according to study co-author Renu Malhotra, a UArizona planetary sciences professor who led the orbit analysis portion of the study.

“It is very unlikely that a garden-variety near-Earth asteroid would spontaneously move into a quasi-satellite orbit like Kamo`oalewa’s,” said Malhotra, whose lab is working on a paper to further investigate the asteroid’s origins. “It will not remain in this particular orbit for very long, only about 300 years in the future, and we estimate that it arrived in this orbit about 500 years ago.”

Kamo`oalewa is about 4 million times fainter than the faintest star the human eye can see in a dark sky.

“These challenging observations were enabled by the immense light-gathering power of the twin 8.4-meter telescopes of the Large Binocular Telescope,” said study co-author Al Conrad, a staff scientist for the telescope.

The study also included data from the Lowell Discovery Telescope in Flagstaff, Arizona. Other co-authors on the paper include Olga KuhnChristian VeilletBarry Rothberg and David Thompson from the Large Binocular Telescope; Audrey Thirouin from Lowell Observatory; and Juan Sanchez from the Planetary Science Institute in Tucson. The research was funded by NASA’s Near-Earth Object Observations Program.

Featured image: An artist’s impression of Earth quasi-satellite Kamo`oalewa near the Earth-moon system. Using the Large Binocular Telescope, astronomers have shown that it might be a lost fragment of the moon.Addy Graham/University of Arizona

Provided by University of Arizona

Simulations Provide Clue To Missing Planets Mystery (Planetary Science)

Forming planets are one possible explanation for the rings and gaps observed in disks of gas and dust around young stars. But this theory has trouble explaining why it is rare to find planets associated with rings. New supercomputer simulations show that after creating a ring, a planet can move away and leave the ring behind. Not only does this bolster the planet theory for ring formation, the simulations show that a migrating planet can produce a variety of patterns matching those actually observed in disks.

Young stars are encircled by protoplanetary disks of gas and dust. One of the world’s most powerful radio telescope arrays, ALMA (Atacama Large Millimeter/submillimeter Array), has observed a variety of patterns of denser and less dense rings and gaps in these protoplanetary disks. Gravitational effects from planets forming in the disk are one theory to explain these structures, but follow-up observations looking for planets near the rings have largely been unsuccessful.

In this research a team from Ibaraki University, Kogakuin University, and Tohoku University in Japan used the world’s most powerful supercomputer dedicated to astronomy, ATERUI II at the National Astronomical Observatory of Japan, to simulate the case of a planet moving away from its initial formation site. Their results showed that in a low viscosity disk, a ring formed at the initial location of a planet doesn’t move as the planet migrates inwards. The team identified three distinct phases. In Phase I, the initial ring remains intact as the planet moves inwards. In Phase II, the initial ring begins to deform and a second ring starts forming at the new location of the planet. In Phase III, the initial ring disappears and only the latter ring remains.

Simulations provide clue to missing planets mystery
A comparison of the three phases of ring formation and deformation found in these simulations by ATERUI II (top) with real examples observed by ALMA (bottom). The dotted lines in the simulation represent the orbits of the planets, and the gray areas indicate regions not covered by the computational domain of the simulation. In the upper row, the simulated protoplanetary disks are shown from left to right at the start of planetary migration (Phase I), during planetary migration (Phase II), and at the end of planetary migration (Phase III). Credit: Kazuhiro Kanagawa, ALMA (ESO/NAOJ/NRAO)

These results help explain why planets are rarely observed near the outer rings, and the three phases identified in the simulations match well with the patterns observed in actual rings. Higher resolution observations from next-generation telescopes, which will be better able to search for planets close to the central star, will help determine how well these simulations match reality.

These results appeared as K.D. Kanagawa et al. “Dust rings as a footprint of planet formation in a protoplanetary disk” in The Astrophysical Journal on November 12, 2021.

Featured image: A protoplanetary disk as observed by ALMA (left), and a protoplanetary disk during planetary migration, as obtained from the ATERUI II simulation (right). The dashed line in the simulation represents the orbit of a planet, and the gray area indicates a region not covered by the computational domain of the simulation. Credit: Kazuhiro Kanagawa, ALMA(ESO/NAOJ/NRAO)

More information: K.D. Kanagawa et al, Dust rings as a footprint of planet formation in a protoplanetary disk, The Astrophysical Journal (2021). arXiv:2109.09579 [astro-ph.EP]

Provided by National Institutes of Natural Sciences