Tag: black hole

Astronomers: A black hole weighing 8,200 solar masses likely sits at the center of the Milky Ways’ largest globular cluster

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Omega Centauri
Click for original image.

By analyzing the motion of seven fast moving stars at the center of the globular cluster Omega Centauri, the largest such cluster in the Milky Way and located about 18,000 light years away, astronomers now think they have detected evidence of an intermediate-sized black hole weight at least 8,200 solar masses.

You can read the published paper here. [pdf] The picture of Omega Centauri to the right, reduced and sharpened to post here, was created from more than 500 images taken over two decades by the Hubble Space Telescope. The inset, figure 1b of the paper, shows those seven fast-moving stars in pink, each having an arrow indicating the distance they are expected to move in a 100 years. The dashed circle marks the region where the black hole is believed to reside, with the dark blue cross in its upper left quadrant the most likely position of the black hole based on calculations.

From the caption for the larger Omega Centauri Hubble image:

Omega Centauri is visible from Earth with the naked eye and is one of the favourite celestial objects for stargazers in the southern hemisphere. Although the cluster is 17 700 light-years away, lying just above the plane of the Milky Way, it appears almost as large as the full Moon when seen from a dark rural area.

Though such intermediate-sized black holes have been theorized as existing inside globular clusters, I think this is the first real evidence of one.

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The 1st image of a black hole’s magnetic field

8:54 am

The magnetic field lines of a black hole

Using the data from the first image of a black hole, obtained in 2019, scientists have now extracted evidence of the magnetic field lines near the event horizon, and from this produced the first image of such lines.

The image to the left, reduced to post here, shows the spiraling magnetic field lines against the bright event horizon ring.

As the Event Horizon Telescope (EHT) team describes today in a pair of papers in Astrophysical Journal, the new picture uses the same data as in the original image, produced from a series of observations in 2017 of the supermassive black hole at the core of nearby galaxy M87, using the combined collecting power of eight radio observatories across the world. To extract the polarization information, the data have gone through many months of additional analysis.

The scientists also note that the orientation of the field lines might eventually help explain the jets being thrown from its poles.

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“Spots” orbiting Milky Ways central black hole

9:19 am

Using the ALMA ground-based telescope array in Chile, astronomers have detected two energetic “spots” that appear to be orbiting Sagittarius A* (pronounced A-star), the super-massive black hole at the center of the Milky Way.

The spots appear to be regions in the accretion disk surrounding the black hole that are emitting energy.

Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.

The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.

Everyone please repeat after me: Though this scenario makes sense, based on the facts and our knowledge, there is a lot of uncertainty about these conclusions.

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Planet X a small black hole?

8:13 am

In one of the wilder theories attempting to explain the orbits of the outer objects found beyond Neptune, two physicists have proposed that the reason Planet X has not been located is because it might be a small black hole.

Previous studies have suggested Planet Nine, which some astronomers refer to as “Planet X,” has a mass between five and 15 times that of Earth and lies between 45 billion and 150 billion kilometers from the sun. At such a distance, an object would receive very little light from the sun, making it hard to see with telescopes.

To detect objects of that mass, whether planets or black holes, astronomers can look for weird blobs of light formed when light “bends” around the object’s gravitational field on its journey through the galaxy (simulated image above). Those anomalies would come and go as objects move in front of a distant star and continue in their orbit.

But if the object is a planet-mass black hole, the physicists say, it would likely be surrounded by a halo of dark matter that could stretch up to 1 billion kilometers on every side. And interactions between dark matter particles in that halo—especially collisions between dark matter and dark antimatter—could release a flash of gamma rays that would betray the object’s presence, the researchers propose in a forthcoming paper posted on the preprint server arXiv.

Anything is possible, but some things are certainly less likely than others. If these scientists turn out to be right, however, they will have achieved one of the biggest coups in the history of science.

And yes, the undiscovered planet out there should be referred to as “Planet X”, not “Planet Nine.” Not only is Pluto a planet, so are a lot of other objects in the solar system that up to recently were not considered so.

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Neutron star merger caused gravitational wave?

10:17 am

The uncertainty of science: Astronomers now believe that one of the half dozen or so gravitational waves detected by LIGO was likely caused by the merger of two neutron stars.

One of these, GW170817, resulted from the merger of two stellar remnants known as neutron stars. These objects form after stars much more massive than the Sun explode as supernovae, leaving behind a core of material packed to extraordinary densities.

At the same time as the burst of gravitational waves from the merger, observatories detected emission in gamma rays, X-rays, ultraviolet, visible light, infrared and radio waves – an unprecedented observing campaign that confirmed the location and nature of the source.

The initial observations of GW170817 suggested that the two neutron stars merged into a black hole, an object with a gravitational field so powerful that not even light can travel quickly enough to escape its grasp.

While intriguing, this result is uncertain, and based on many assumptions.

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Baby stars at center of galaxy

2:40 pm

New observations of the region surrounding Sagittarius A* (Sgr A*), the super-massive black hole at the center of the Milky Way, has confirmed earlier research by finding what appears to be eleven newly formed baby stars.

Prior observations of the region surrounding Sgr A* by Zadeh and his team had revealed multiple massive infant stars but the finding was not conclusive. These objects, known as proplyds, are common features in more placid star-forming regions, like the Orion Nebula. The new measurements provide more conclusive evidence for young star formation activity. Though the galactic center is a challenging environment for star formation, it is possible for particularly dense cores of hydrogen gas to cross the necessary threshold and forge new stars.

The new ALMA observations, however, revealed something even more remarkable, signs that 11 low-mass protostars are forming within one parsec – a scant three light-years – of the galaxy’s central black hole. Zadeh and his team used ALMA to confirm that the masses and momentum transfer rates – the ability of the protostar jets to plow through surrounding interstellar material – are consistent with young protostars found throughout the disk of our galaxy. “This discovery provides evidence that star formation is taking place within clouds surprisingly close to Sagittarius A*,” said Al Wootten with the National Radio Astronomy Observatory in Charlottesville, Virginia, and co-author on the paper.

They have several theories on how new stars could coalesce in such a violent and turbulent region, but none appears that convincing. Essentially, this is a mystery that does not yet have an answer. It does tell us however that star formation can occur almost anywhere.

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Star becomes black hole without supernova explosion

10:20 am

The uncertainty of science: Astronomers think they have identified a star that, rather than die and become a black hole in a supernova explosion, merely fizzled into a black hole.

Starting in 2009, one particular star in the Fireworks Galaxy, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence. The astronomers aimed the Hubble Space Telescope at the star’s location to see if it was still there but merely dimmed. They also used the Spitzer Space Telescope to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole.

There are a lot of uncertainties here. Nonetheless, astronomers have theorized that some stars could collapse into black holes with any explosions, and it appears they might have found their first example of that.

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Did a giant black hole eat a star?

10:45 am

New data now suggests that what astronomers had thought was the brightest supernova ever detect might have instead been the ripping apart of a star as it passed too close to a supermassive black hole.

In this scenario, the extreme gravitational forces of a supermassive black hole, located in the centre of the host galaxy, ripped apart a Sun-like star that wandered too close — a so-called tidal disruption event, something so far only observed about 10 times. In the process, the star was “spaghettified” and shocks in the colliding debris as well as heat generated in accretion led to a burst of light. This gave the event the appearance of a very bright supernova explosion, even though the star would not have become a supernova on its own as it did not have enough mass. The team based their new conclusions on observations from a selection of telescopes, both on the ground and in space. Among them was the NASA/ESA Hubble Space Telescope, the Very Large Telescope at ESO’s Paranal Observatory and the New Technology Telescope at ESO’s La Silla Observatory

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It turns out that the object dubbed G2 that is zipping past the Milky Way’s central black hole is behaving not like a cloud but more like a star.

10:24 pm

The uncertainty of science: It turns out that the object dubbed G2 that is zipping past the Milky Way’s central black hole is behaving not like a cloud but more like a star.

The latest observations by the Keck Observatory in Hawaii show that the gas cloud called “G2” was surprisingly still intact, even during its closest approach to the supermassive black hole at the center of our Milky Way galaxy. Astronomers from the UCLA Galactic Center Group reported today that observations obtained on March 19 and 20, 2014 show the object’s density was still “robust” enough to be detected. This means G2 is not just a gas cloud, but likely has a star inside.

When I wrote a piece about this object for Sky & Telescope I found that among astronomers there was great skepticism about it being just a gas cloud that would be ripped apart when it flew past the black hole. The early data was not conclusive, but enough of it suggested G2 was a star, not a cloud. It turns out here that the skeptics were right.

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The biggest black hole yet found, 17 billion times the mass of our sun.

12:00 pm

The biggest black hole yet found, 17 billion times the mass of our sun.

The unusual black hole makes up 14 percent of its galaxy’s mass, rather than the usual 0.1 percent. … NGC 1277 [the galaxy] lies 220 million light-years away in the constellation Perseus. The galaxy is only ten percent the size and mass of our own Milky Way. Despite NGC 1277’s diminutive size, the black hole at its heart is more than 11 times as wide as Neptune’s orbit around the Sun.

Based on these measurements, it appears that this black hole is literally eating this galaxy whole.

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The supermassive black hole in the center of the Milky Way is about to get a snack.

6:16 pm

The supermassive black hole in the center of the Milky Way is about to get a snack.

Update: The recently launched NuStar telescope in July detected its first flare from the central black hole (which by the way is called Sagittarius A* and is pronounced Sagittarius A-star). If the gas cloud produces any fireworks as it whips past the black hole in the coming year then NuStar should see it.

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Astronomers have discovered a star that circles the supermassive black hole at the center of the Milky Way in only 11.5 years.

5:57 pm

Dizzy: Astronomers have discovered a star that circles the supermassive black hole at the center of the Milky Way in only 11.5 years.

This newly discovered star joins another that is 15 times brighter and has a 16 year orbit. The combined orbital data from both will allow astronomers to measure precisely the size of the black hole while also measuring the distortion of space caused by its intense gravitational field.

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