Hubble finds a density of small black holes

Astronauts discovered something they did not intend to be at the heart of the NGC 6397 universe: a density of smaller black holes lying there instead of one large black hole.

Global clusters are close-knit systems, which host stars that are crowded together. These systems are usually very old – the global browser at the focus of this study, NGC 6397, is almost as old as the universe itself. This collection lives 7,800 light-years away, making it one of the closest global collections to Earth. Because of its highly dense nucleus, it is known as a body that collapsed to the heart.

Initially, astronomers thought that the spherical assemblage hosted an intermediate black hole. These are the long-standing “missing link” between massive black holes (millions of times our solar mass) that lie at the heart of galaxies, and stellar-mass black holes (a few times our solar mass) that which forms after the fall of one large star. There is a strong debate about existence. Only a few candidates have been identified so far.

“We found very strong evidence for an invisible mass in the dense heart of the globular globe, but were surprised to discover that this extra mass does not look like a point (one would expect a large, isolated black hole). but expanded to a few percent of browser size, “said Eduardo Vitral of the Paris Institute of Astrophysics (IAP) in Paris, France.

To find the hidden mass that cannot be discovered, Vitral and Gary Mamon, also of IAP, used the speeds of the stars in the cluster to determine the rotation of its total mass, the mass in the visible stars, which as well as in narrow stars and black holes. The larger the mass somewhere, the faster the stars travel around it.

The researchers used previous estimates of the tiny movements of the stars (the similar movements in the sky), which allow to determine the true velocities within the cluster. These precise measurements for stars in the heart of the cluster could only be made by Hubble over several years of observation. The Hubble data was added to accurate, well-rated motion measurements provided by the European Space Agency’s Gaia space observatory that are less accurate than the Hubble observations at heart.

“Our analysis showed that the orbits of the stars are almost random across the globe, rather than being systemically or very long,” Mamon explained. These medium-long orbital shapes limit what is needed. the inner mass being.

The researchers conclude that the invisible part can only be made up of the remains of large stars (white dwarfs, neutron stars, and black holes) because of its size, dimension, and location. These stellar bodies were gradually sunk to the center of the cluster after gravity interactions with smaller nearby stars. This game of stellar pinball is called “dynamic counterpoint”, where, through the exchange of momentum, heavier stars are separated in the heart of the cluster and large lower stars migrate to cluster margin.

“We used stellar evolutionary theory to conclude that most of the extra mass we found was in the shape of a black hole,” Mamon said. Two other recent studies also suggested that stellar debris, particularly large stellar black holes, could capture internal regions of spherical assemblages. “We are the first study to give both the mass and extent of what appears to be a predominantly black hole collection in the middle of a collapsed global browser,” Vitral said.

The astronomers also note that this discovery raises the possibility that the unification of these black holes full of folds in spherical assemblages could be an important source of gravitational waves, passing through space time. . Such a phenomenon could be detected by the Gravitational-Wave Laser Interferometer Observation test, which is funded by the National Science Foundation and run by Caltech in Pasadena, California and MIT in Cambridge, Massachusetts.

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The Hubble Space Telescope is a project of international collaboration between NASA and ESA (European Space Agency). The telescope will be controlled by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science activity. STScI is run for NASA by the Association of Universities for Research in Astronomy in Washington, DC

Image credit: NASA, ESA, T. Brown, S. Casertano, and J. Anderson (STScI)

Science Credit: NASA, ESA, and E. Vitral and G. Mamon (Institut d’Astrophysique de Paris (IAP))