Accretion disk around our galaxy’s ‘black hole’ spotted at last
ORGANIZED CHAOS The black hole in the center of the Milky Way has a chaotic entourage of stars and gas, shown here in X-ray light. But new observations with the ALMA telescope array show a relatively neat disk of glowing gas rotating around the black hole.
Some supermassive black holes announce their presence with screaming hot disks of orbiting gases. But the behemoth at the center of the Milky Way has been shy and demure. Now, astronomers have finally spotted the black hole’s faintly glowing accretion disk of infalling material, long suspected but never before seen.
“I was very surprised that we actually saw it,” says astrophysicist Elena Murchikova at the Institute for Advanced Study in Princeton, N.J. The disk was observed using the Atacama Large Millimeter/submillimeter Array, or ALMA, in northern Chile, the researchers report in the June 6 Nature.
The Milky Way’s supermassive black hole, named Sagittarius A*, is a behemoth at 4 million solar masses. But while some black holes gobble the gas and dust around them, Sgr A* picks daintily. Such “underfed” black holes “don’t have enough food supply” for their surrounding gases to glow brightly, Murchikova says.
LIKE A RECORD This image made from ALMA data shows that some of the gas orbiting the Milky Way’s black hole is moving toward Earth (colored blue), and some is moving away (red). That finding means that the disk is spinning. The plus sign indicates the position of the black hole.
The disk’s diminished glow helps explain why scientists with the Event Horizon Telescope were able to capture a picture of the central black hole in the more distant galaxy M87, but not yet Sgr A* (SN: 4/27/19, p. 6).Previously, scientists had seen a cloud of hot gas (around 10 million kelvins) emitting high-energy X-rays around Sgr A*, as well as stars and gas clouds circling the black hole. But those gas sources didn’t seem to be organized into a neat, orbiting disk. Murchikova and colleagues focused their search on cooler gases, about 10,000 kelvins, located within about 280 billion kilometers of Sgr A*. Looking at only the hot gas, she explains, is like trying to study Earth’s climate by focusing on summers in the desert. “Gas of both types should be falling into the black hole,” Murchikova says. “You need a full picture.”
ALMA measured the cooler gases by observing particles of light in a particular wavelength. Those photons are emitted when electrons and protons in the gases combine to form hydrogen atoms. When Murchikova and colleagues looked at the photon distribution around the black hole, they saw an oblong disk with a gap in the middle where the black hole sits.
On one side of the disk, the light wavelength was stretched, or redshifted. On the other side, the light was squished, or blueshifted. That finding means that one side of the disk is moving toward Earth, and the other is moving away — a clear sign that the disk is rotating.
“I never thought I would actually be able to see such an organized rotation,” Murchikova says.
The team also estimated the disk’s mass — between 0.00001 and 0.0001 times the mass of the sun, depending on how thick the disk might be. And the researchers estimated how much material is falling into the black hole, which they say is about 2.7×10-10 solar masses per year, or roughly about half the mass of the dwarf planet Ceres.
“I think it’s very exciting,” says astrophysicist Anna Ciurlo of UCLA, who was not involved in the new work. Her team has used the Keck telescope in Hawaii to look for signs of the disk in infrared wavelengths, but found nothing.
If the disk’s activity can be picked up by ALMA, but not Keck, that “makes us think there’s some more peculiar process going on that is not totally understood yet,” Ciurlo says. More observations with ALMA and with the Event Horizon Telescope could help resolve the mystery.
Read more at www.sciencenews.org
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Robert Beatty
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Herb,
“The complications of Newton’s and Einsteins include the necessities of creating potential energy, dark matter, dark energy, black holes, singularities, making time and distance variables, and the creation of many particles to preserve them that are not a result of evidence but of theory.”
Can we take black holes off this list now?
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Herb Rose
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Hi Robert,
I will keep it on my list. If the black hole is at the center of the Milky Way then we are orbiting around it in a fairly circular path meaning our distance from it is fairly constant. Why the red and blue shift? The light is being emitted by material falling into the black hole. Why is it rotating with angular velocity also?
The problem with looking for things you believe exists is that any unexpected observation is taken as evidence supporting your belief. This is why I believe accelerators produce crap science. They always find what they are looking for.
Herb
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Robert Beatty
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Herb,
“Why the red and blue shift? The light is being emitted by material falling into the black hole. Why is it rotating with angular velocity also?”
Surely it would be more unusual if it was not rotating before it disappears into the black hole. Just like water going down a faucet?
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Herb Rose
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Hi Robert,
The particles emitting light are the ones dropping into the drain not the ones in the sink waiting to drop in the drain. I believe that the author thinks the red and blue shift are due to a Doppler effect while we believe they are due to a change in the speed of light. How does your belief that gravitational forces on light from black holes causes these shifts explain both a red and blue shift so close to a black hole? I have no explanation for it and consider it one of those mysteries we encounter where we should not look for an excuse to serve as an answer until we have more information.
Herb
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Robert Beatty
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Herb,
The ‘ALMA is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths.’
The light image you refer to is an IT interpretation of these invisible radio waves which shows one side of the event horizon has material moving away from our observation perspective while the other side is moving towards us. The black hole is in-between these two images and not directly visible – as it is in the image recently shown on PSI, obtained from the black hole in Messier 87’s galactic centre.
Now can we cross black holes and singularities off your “evil list of eight”?
Herb Rose
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Hi Robert,
You can’t see electromagnetic waves traveling away from you, only those traveling towards you. Wouldn’t’ the black hole act as light sink preventing any light from the far side crossing it and reaching us?
I believe in areas where we see no light but not “black holes” where gravity is preventing light from escaping. Just recently there was talk of empty areas of space where there were no light visible. Improvements in telescopes showed these empty areas were full of stars and galaxies.
The sun radiates light, a magnetic field, and an electrical field in all directions. All the other stars in the Milky Way do the same. Geometry says that the light and fields of all the stars in the Milky Way will converge at the center of the galaxy. If two light beams going in the same direction (Young experiment) can produce dark bands where the interference between light beams cancel each other out what kind of interference would occur at the center of the galaxy where light is converging from all directions?
Herb
Robert Beatty
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Herb,
“You can’t see electromagnetic waves traveling away from you, only those traveling towards you. Wouldn’t’ the black hole act as light sink preventing any light from the far side crossing it and reaching us?”
The electromagnetic rays travel in all directions. We just pick up a slower or quicker reading which has been interpreted as blue or red. The blue image represents material that is accelerating as it passes the high gravity influence of the bh and the red represents slowing as it moves away from the bh high gravity region.
The bh itself is not evident in this image because our solar system is on an arm of the milky-way galaxy while this image comes from the centre which is therefore notoriously difficult to see. Even more so given the text which reports Sgr-A only operates spasmodically.
Interesting to compare this image with Messier 87 where the bh is quite evident. This suggest to me that a bh is a cylindrical structure or egg shaped with cosmic rays seen coming out of both ends. The bh is only visible when viewed down the cylinder axis.
I doubt that all the stars in our galaxy could be so well coordinated to produce a light cancelling black spot at the centre? Much more likely to be the elusive bh.
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Herb Rose
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Hi Robert,
Despite the difficulty in seeing the center of the galaxy we accept these images as accurate even though they have gone through extensive interpretation and editing. We know that electromagnetic waves bend or are distorted when passing close to stars (either by gravity or stronger electric and magnetic fields). How can these distortions be adjusted for or even known?
Light waves don’t need to be coordinated to produce interference, just of the same wave length and be out of phase. We only see images where there is no interference. At a different distance from an object we will see a similar image but it is produced by different light waves since the light waves of producing the first image experience interference and the image is erased.
Herb
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Robert Beatty
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Thanks Herb,
I think the most important finding from this conversation was: “This suggest to me that a bh is a cylindrical structure or egg shaped with cosmic rays seen coming out of both ends. The bh is only visible when viewed down the cylinder axis.”
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Herb Rose
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Doug
The only thing anyone sees is electromagnetic waves. In this case, the electromagnetic waves are radio waves seen by antennas and represented by different colors by computer images.
Why do you persist in using aliases like DC, Physicist, Physic Teacher, Atmospheric Scientist, etc.instead of your name. Is it to avoid having your comments deleted or so you can refer to yourself as “brilliant” hiding your egotism?
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