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A Comparison of Black Holes

“A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole.” – Wikipedia



Scientists detected collision between a black hole and a neutron star for the first time

Strong gravitational waves recorded by the LIGO and Virgo observatories have revealed what experts believe may be the first detection of a neutron star swallowed by a black hole or we can say a collision between a black hole and a neutron star.

collision between a black hole and a neutron star

The historical event, which was detected on August 14 and received the name S190814bv, was recorded on Wednesday in a public database used by astronomers. The initial analysis suggests that there is a 99 percent chance that the waves are the consequences of the cataclysmic fusion of a neutron star with a black hole.

“So far, it obviously does not resemble anything we have detected very safely before,” Daniel Holz, a scientist at the University of Chicago and a member of LIGO, told Science News. He believes that potential detection is already exciting on its own. “The first of anything is always really fascinating,” he added.

Scientists are still analyzing the data to verify what generated gravitational waves. If the assumptions are confirmed, this would be the first solid detection of a type of phenomenon never seen before. The researchers estimate that the clash between the two objects occurred about 900 million light-years away.

Source:  Science News.

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Our Galaxy’s Black Hole Suddenly Lit Up and Nobody Knows Why

In May, the supermassive black hole at the core of the Milky Way became 75 times brighter in just two hours.

The supermassive black hole that lives at the center of our galaxy has been mysteriously sparkling as of late, and nobody knows the reason.

This dark behemoth, known as as Sagittarius A* (Sgr A*), is four million times as massive as the Sun. Though no light escapes its boundaries, astronomers can observe the hole’s interactions with bright stars or dust clouds that surround it.

On the night of May 13, 2019, UCLA astronomer Tuan Do and his colleagues were watching Sgr A* using the Keck Telescope on the summit of Mauna Kea in Hawai’i. In a period of just two hours, they witnessed the black hole become 75 times brighter in the near-infrared band of the light spectrum.

That spring evening, the Milky Way’s supermassive black hole “reached much brighter flux levels in 2019 than ever measured at near-infrared wavelengths,” according to a forthcoming studyled by Do and published on the arXiv preprint server.

“The brightness of Sgr A* varies all the time, getting brighter and fainter on the timescale of minutes to hours—it basically flickers like a candle,” Do said in an email. “We think that something unusual might be happening this year because the black hole seems to vary in brightness more, reaching brighter levels than we’ve ever seen in the past.”

The peak flux, meaning the most luminous phase of the flare-up, soared to “twice the maximum historical flux measurements,” Do’s team said in the study. In other words, in the 20 years since astronomers have monitored Sgr A*, the next-brightest event has only been half as dazzling as this one.

This unusual sparkle at the galactic core was likely caused by close encounters between Sgr A* and objects surrounding it, according to the team.

The edge of a black hole, called an event horizon, is shaped by intense tidal forces that tear at anything that gets close. Once a black hole starts devouring nearby objects like stars or gas clouds, infalling material heats up at the event horizon, sparking light shows that can be picked up by telescopes.

Do and his colleagues speculate that a star called S0-2, which is about 15 times as massive as the Sun, may have been the object that juiced Sgr A*. In 2018, S0-2 came within 17 light hours of the supermassive black hole, and that close pass may have disturbed gases at the event horizon enough to cause the May 2019 brightening event.

This composite image shows the motion of the dusty cloud G2 as it closes in on, and then passes, the supermassive black hole at the centre of the Milky Way. These new observations with ESO’s VLT have shown that the cloud appears to have survived its close encounter with the black hole and remains a compact object that is not significantly extended. In this image the position of the cloud in the years 2006, 2010, 2012 and February and September 2014 are shown, from left to right. The blobs have been colourised to show the motion of the cloud, red indicated that the object is receding and blue approaching. The cross marks the position of the supermassive black hole.

Another possible culprit is a dust cloud known as G2, which passed about 36 light hours from Sgr A* in 2014. Scientists predicted that G2 would be torn apart by the hole, but the results were ultimately described as disappointing and “boring” for astronomers.

That initial letdown may have been premature, though, because we might be seeing the slow-burn “delayed reaction” to the gas cloud’s approach, the team said.

“Many astronomers are observing Sgr A* this summer,” Do noted. “I’m hoping we can get as much data as we can this year before the region of the sky with Sgr A* gets behind the Sun and we won’t be able to observe it again until next year.”

“Maybe the black hole is waking up—there’s a lot we don’t know at this point so we need more data to understand if what we are seeing is a big change in what is feeding the black hole or this is a brief event,” he said.


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Milky Way galaxy is warped and twisted, not flat

Our galaxy, the Milky Way, is “warped and twisted” and not flat as previously thought, new research shows.

Analysis of the brightest stars in the galaxy shows that they do not lie on a flat plane as shown in academic texts and popular science books.

Astronomers from Warsaw University speculate that it might have been bent out of shape by past interactions with nearby galaxies.

The new three dimensional map has been published in the journal Science.

The popular picture of the Milky Way as a flat disc is based on the observation of 2.5 million stars out of a possible 2.5 billion. The artists’ impressions are therefore rough approximations of the truer shape of our galaxy, according to Dr Dorota Skowron of Warsaw University.

“The internal structure and history of the Milky Way is still far from being understood, in part because it is extremely difficult to measure distances to stars at the outer regions of our galaxy,” she said.

To gain a more accurate picture, Dr Skowron and her colleagues measured the distances of some of the brightest stars in the Milky Way, called Cepheid variable stars. These are massive young stars that burn hundreds, if not thousands, of times brighter than our own Sun. They can be so bright that they can be observed at the very edge of the galaxy.

Not only that, they also pulsate at regular intervals at a rate that is directly related to their brightness.

Artists’ impressions which depict the Milky Way as a flat disk will have to be revised

This enables astronomers to calculate their distance with great precision.

Most of the stars were identified by the Optical Gravitational Lensing Experiment (OGLE) at Las Campanas Observatory (LCO) in Chile’s southern Atacama Desert. Przemek Mroz, a member of the OGLE team, said that the results were surprising.

Warsaw Telescope and Milky Way Cepheids discovered by the OGLE survey

“Our results show that the Milky Way Galaxy is not flat. It is warped and twisted far away from the galactic centre. Warping may have happened through past interactions with satellite galaxies, intergalactic gas or dark matter (invisible material present in galaxies about which little in known).”

The Polish results support an analysis of Cepheid variable stars published in February in Nature Astronomy journal by astronomers from Macquarie University in Australia and the Chinese Academy of Sciences.


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