Black Holes

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The supermassive black hole at the center of our galaxy is binge eating.
https://phys.org/news/2019-09-black-hole-center-galaxy-hungrier.html
The enormous black hole at the center of our galaxy is having an unusually large meal of interstellar gas and dust, and researchers don't yet understand why.

"We have never seen anything like this in the 24 years we have studied the supermassive black hole," said Andrea Ghez, UCLA professor of physics and astronomy and a co-senior author of the research. "It's usually a pretty quiet, wimpy black hole on a diet. We don't know what is driving this big feast."

A paper about the study, led by the UCLA Galactic Center Group, which Ghez heads, is published today in Astrophysical Journal Letters.

The researchers analyzed more than 13,000 observations of the black hole from 133 nights since 2003. The images were gathered by the W.M. Keck Observatory in Hawaii and the European Southern Observatory's Very Large Telescope in Chile. The team found that on May 13, the area just outside the black hole's "point of no return" (so called because once matter enters, it can never escape) was twice as bright as the next-brightest observation.

They also observed large changes on two other nights this year; all three of those changes were "unprecedented," Ghez said.

The brightness the scientists observed is caused by radiation from gas and dust falling into the black hole; the findings prompted them to ask whether this was an extraordinary singular event or a precursor to significantly increased activity.

"The big question is whether the black hole is entering a new phase—for example if the spigot has been turned up and the rate of gas falling down the black hole 'drain' has increased for an extended period—or whether we have just seen the fireworks from a few unusual blobs of gas falling in," said Mark Morris, UCLA professor of physics and astronomy and the paper's co-senior author.
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You Cannot Conceive of the Hugeness of This Black Hole

www.youtube.com/watch?v=zo9rNHcF41U
In space, black holes appear in different sizes and masses. The record is now held by a specimen in the Abell 85 cluster of galaxies, where an ultra-massive black hole with 40 billion times the mass of our Sun sits in the middle of the central galaxy Holm 15A. Astronomers at the Max Planck Institute for Extraterrestrial Physics and the University Observatory Munich discovered this by evaluating photometric data from the Wendelstein Observatory as well as new spectral observations with the Very Large Telescope.

Even though the central galaxy of the cluster Abell 85 has the enormous visible mass of about 2 trillion (10^12) solar masses in stars, the centre of the galaxy is extremely diffuse and faint. This is why a joint group of astronomers at the Max Planck Institute for Extraterrestrial Physics (MPE) and the University Observatory Munich (USM) got interested in the galaxy. This central diffuse region in the galaxy is almost as large as the Large Magellanic Cloud, and this was a suspicious clue for the presence of a black hole with a very high mass.

The Abell 85 cluster of galaxies, which consists of more than 500 individual galaxies, is at a distance of 700 million light-years 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 new data obtained at the USM Wendelstein observatory of the Ludwig-Maximilians-University and with the MUSE instrument at the VLT allowed the team to perform a mass estimate based directly on the stellar motions around the core of the galaxy. With a mass of 40 billion solar masses, this is the most massive black hole known today in the local universe. “This is several times larger than expected from indirect measurements, such as the stellar mass or the velocity dispersion of the galaxy,” remarks Roberto Saglia, senior scientist MPE and lecturer at the LMU.

The light profile of the galaxy shows a centre with an extremely low and very diffuse surface brightness, much fainter than in other elliptical galaxies. “The light profile in the inner core is also very flat,” explains USM doctoral student Kianusch Mehrgan, who performed the data analysis. “This means that most of the stars in the centre must have been expelled due to interactions in previous mergers.”

In the commonly accepted view, the cores in such massive elliptical galaxies form via so-called “core scouring”: In a merger between two galaxies the gravitational interactions between their merging, central black holes lead to gravitational slingshots that eject stars on predominantly radial orbits from the centre of the remnant galaxy. If there is no gas left in the centre to form new stars -- as in younger galaxies -- this leads to a depleted core.

“The newest generation of computer simulations of galaxy mergers gave us predictions that do indeed match the observed properties rather well,” states Jens Thomas, who also provided the dynamical models. “These simulations include interactions between stars and a black hole binary, but the crucial ingredient is two elliptical galaxies that already have depleted cores. This means that the shape of the light profile and the trajectories of the stars contain valuable archaeological information about the specific circumstances of core formation in this galaxy -- as well as other very massive galaxies.”

However, even with this unusual merging history, the scientists could establish a new and robust relation between the black hole mass and the galaxy’s surface brightness: With every merger the black hole gains mass and the galaxy centre loses stars. Astronomers could use this relation for black hole mass estimates in more distant galaxies, where direct measurements of the stellar motions close enough to the black hole are not possible.
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The sky is full of weird X-shaped galaxies. Here’s why. | Live Science
Spied through a normal telescope, the galaxy PKS 2014−55 is an unremarkable smudge of bright light. But look again in radio wavelengths, and you'll see that the galaxy is hiding a gargantuan, glowing treasure at its center — and X marks the spot.


PKS 2014−55 is an X-shaped radio galaxy (XRG), an unusual type of galaxy that looks like an enormous X in the night sky when imaged in radio wavelengths. The long arms of the X — each one about 100 times longer than the Milky Way — are actually a blazing-fast soup of particles and magnetic fields, blasted out of the galaxy's central black hole and traveling for millions of light-years into space, far beyond the galaxy's edge.

Big jets of radio energy are common in galaxies with hungry black holes at their centers (even the Milky Way has two "bubbles" of radio energy around its gut). However, most of those jets come in orderly pairs that appear to form a straight line or a round bulge when seen from far away. According to William Cotton, an astronomer at the National Radio Astronomy Observatory (NRAO) in Virginia who studies XRGs, fewer than 10% of known cosmic radio sources take on a distinct X shape like this one.



Related: The biggest black hole findings of 2019


"You see four things poking out of this galaxy," Cotton, lead author of a new study on the galaxy, told Live Science, "and the question is, how did it get that way?"


Now, Cotton and his colleagues may have an answer. In a new study posted May 7 on the pre-print server arXiv and accepted for publication in the journal Monthly Notices of the Royal Astronomical Society, researchers with the NRAO and South African Radio Astronomy Observatory (SARAO) used the massive MeerKAT radio telescope in South Africa's Karoo desert to capture the most detailed image of an XRG ever. The image, shown above, reveals that the strange X bursting out of PKS 2014−55's center apparently isn't an X at all.

"It's actually a 'double boomerang' shape," Cotton said. "That means something in the galaxy is diverting the flow into these secondary wings."
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Astronomers see a black hole 'spaghettify' and swallow a star in real time

www.youtube.com/watch?v=AKCp-1OGGP4&feature=emb_title
This animation depicts a star experiencing spaghettification as it’s sucked in by a supermassive black hole during a ‘tidal disruption event’. In a new study, done with the help of ESO’s Very Large Telescope and ESO’s New Technology Telescope, a team of astronomers found that when a black hole devours a star, it can launch a powerful blast of material outwards.
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