APOD: The Milky Way's Black Hole (2022 May 13)

[APOD Robot]

The Milky Way's Black Hole

Explanation: There's a black hole at the center of the Milky Way. Stars are observed to orbit a very massive and compact object there known as Sgr A* (say "sadge-ay-star"). But this just released radio image (inset) from planet Earth's Event Horizon Telescope is the first direct evidence of the Milky Way's central black hole. As predicted by Einstein's Theory of General Relativity, the four million solar mass black hole's strong gravity is bending light and creating a shadow-like dark central region surrounded by a bright ring-like structure. Supporting observations made by space-based telescopes and ground-based observatories provide a wider view of the galactic center's dynamic environment and an important context for the Event Horizon Telescope's black hole image. The main panel image shows the X-ray data from Chandra and infrared data from Hubble. While the main panel is about 7-light years across, the Event Horizon Telescope inset image itself spans a mere 10 light-minutes at the center of our galaxy, some 27,000 light-years away.

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[bystander]

viewtopic.php?p=322660#p322660

[Ann]

APOD Robot wrote:
While the main panel is about 7-light years across, the Event Horizon Telescope inset image itself spans a mere 10 light-minutes at the center of our galaxy, some 27,000 light-years away.

Just 10 light-minutes? That's just a little bigger than the radius of the Earth's orbit around the Sun. So Sgr A* packs 4.3 million solar masses inside a volume just a little bigger than the Earth's orbit around the Sun.

(Thanks for the pronunciation tip, by the way - I have been saying Sag-gi-tta-ri-us A star, which is unwieldy.)

A question, though. I watched parts of the press conference yesterday, and the lead researchers presenting their conclusions said that the orientation of Sgr A* is face on to us. That is to say that one of its poles is pointing more or less our way. And black holes launch jets, at least sometimes, from the polar regions.

Streaming out from the center of M87 like a cosmic searchlight is one of nature’s most amazing phenomena: a black-hole-powered jet of subatomic particles traveling at nearly the speed of light. In this Hubble image, the blue jet contrasts with the yellow glow from the combined light of billions of unresolved stars and the point-like clusters of stars that make up this galaxy. Credits: NASA and the Hubble Heritage Team (STScI/AURA)

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Active galaxy Cen A is also launching a jet from its black hole. ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray). Derivative work including grading and crop: Julian Herzog.

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What I'm asking is this: If Sgr A* was to suddenly emit a jet, would we be in the firing line?

I'm also wondering how wide such a jet would be. Because the wider it is, the more damage it will do. The picture below of a galaxy actually zapping its neighbor with its long X-ray jet is scary.

(Did a number of emerging civilizations in the smaller galaxy just get wiped out as that million light-year-long jet hit them? Inquiring minds want to know.)

Galaxy 3C321 zapping its smaller neighbor with a long jet. Image: NASA, ESA, D. Evans (Harvard-Smithsonian Center for Astrophysics), [X-ray: NASA/CXC/CfA/D.Evans et al.; Optical/UV: NASA/STScI; Radio: NSF/VLA/CfA/D.Evans et al., STFC/JBO/MERLIN]

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In any case, I'm very grateful that Sgr A* isn't currently active. I think it was said at the press conference that if a human being was eating as peckishly as Sgr A*, he or she would consume one grain of rice in a million years.

A grain of rice. Image: Maciej Toporowicz, NYC/Getty Images

---

No one, neither humans nor black holes, will produce very powerful burps from such a diet!


Ann

[JohnD]

Ann,
"Only ten light-minutes?" Messier 87, the subject of the previous Event Horizon Telescope exploit, has 65 Billion solar masses, whereas Sagittarius A* is less than 5 Million solar masses. So the latter has a much smaller accretion disc.

All,
On the image, that of M87 showed one side of the disc to be brighter, explained by Doppler effect, as the disc spins. The image of SgrA* has three bright patches. Difficult to reconcile that with the same explanation, is there another?

JOhn

[heehae]

Here is my comparison with the previous wonderful Black Hole image: https://henry.pha.jhu.edu/bh.png

[Case]

Just 10 light-minutes? That's just a little bigger than the radius of the Earth's orbit around the Sun.

That makes the ring itself roughly the size of the Mercury orbit.

[JohnD]

Just 10 light-minutes? That's just a little bigger than the radius of the Earth's orbit around the Sun.

That makes the ring itself roughly the size of the Mercury orbit.

Ummmmmmmmmm! Space is awfully big etc. etc, but its darn sight bigger than that!

Ten-light minutes = 1.799e+8 kilometers or 180,000,000 Km
Mercury orbit diameter = 58,000,000 Km
Venus " " = 108,200,000 km
Earth " " = 149,600,000 Km
Mars " " = 228,000,000 Km


So, the accretion disc of SgrA* is almost as big as than Mars' orbit

John

[bystander]

Here is my comparison with the previous wonderful Black Hole image: https://henry.pha.jhu.edu/bh.png

Here's the comparison by the EHT Collaboration over on the ESO page.

Comparison of black hple sizes: M87* & Sgr A* ~ Credit: EHT Collaboration

---

[orin stepanek]

It is amazing what we can see with the instruments man possesses
today!
Milky Ways black hole is enormous; yet it is very small in comparison
withM87! OMG!

[Chris Peterson]

Ann,
"Only ten light-minutes?" Messier 87, the subject of the previous Event Horizon Telescope exploit, has 65 Billion solar masses, whereas Sagittarius A* is less than 5 Million solar masses. So the latter has a much smaller accretion disc.

All,
On the image, that of M87 showed one side of the disc to be brighter, explained by Doppler effect, as the disc spins. The image of SgrA* has three bright patches. Difficult to reconcile that with the same explanation, is there another?

Take the details of the image with a big grain of salt. The image is constructed using statistical methods from radio data, and there are multiple valid solutions (where "valid" doesn't mean "accurate"). Each of those bright spots is about the size of a single "pixel" in the raw data. That is, this image appears much higher resolution than it actually is. Far more important than those apparent bright areas in this image is the overall size and the donut-like appearance. That's what fundamentally supports GR's model of black holes.

This image shows not just today's APOD, but four other equally valid solutions derived from the radio data. And the little white circle shows the resolution.
_

[Chris Peterson]

APOD Robot wrote:
While the main panel is about 7-light years across, the Event Horizon Telescope inset image itself spans a mere 10 light-minutes at the center of our galaxy, some 27,000 light-years away.

Just 10 light-minutes? That's just a little bigger than the radius of the Earth's orbit around the Sun. So Sgr A* packs 4.3 million solar masses inside a volume just a little bigger than the Earth's orbit around the Sun.

(Thanks for the pronunciation tip, by the way - I have been saying Sag-gi-tta-ri-us A star, which is unwieldy.)

A question, though. I watched parts of the press conference yesterday, and the lead researchers presenting their conclusions said that the orientation of Sgr A* is face on to us. That is to say that one of its poles is pointing more or less our way. And black holes launch jets, at least sometimes, from the polar regions.

What I'm asking is this: If Sgr A* was to suddenly emit a jet, would we be in the firing line?

I'm also wondering how wide such a jet would be. Because the wider it is, the more damage it will do. The picture below of a galaxy actually zapping its neighbor with its long X-ray jet is scary.

I don't think jets like that present much danger. They are jets of matter, not high energy particles (such as some supernovas and other phenomena can produce). The jet is a hard vacuum. The material is hot enough to emit x-rays, but x-rays don't penetrate our atmosphere. And, of course, the black hole at the center of our own galaxy is a tiny little thing compared to the SMBs in many galaxies the size of ours.

The evidence is that all SMBs alternate between active and quiescent states, so it's likely ours has gone through many cycles of high activity in the past.

[Fred the Cat]

It may not be feeding but humans can benefit from this news today.

[DL MARTIN]

Now that we've seen the blackhole of our galaxy; if there is danger of a pending emission will we not have 27,000 years to figure out what to do?

[Chris Peterson]

Now that we've seen the blackhole of our galaxy; if there is danger of a pending emission will we not have 27,000 years to figure out what to do?

No. All we know is that it isn't currently very active. We don't know enough about the interaction between SMBs and their surrounding stars to have much idea how long a conversion to high activity would take. That would be how much time we have to prepare (not that it's likely this SMB could do anything that would present any risk to us).

[Spif]

I presume that most (or all?) of those stars are either in the foreground or the background?

[Chris Peterson]

I presume that most (or all?) of those stars are either in the foreground or the background?

Where else could they be?

[Ann]

I presume that most (or all?) of those stars are either in the foreground or the background?

Where else could they be?

Perhaps some of them could be at the same distance to us as Sgr A*, to the east or left of Sgr A*?

This composite colour infrared image of the centre of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionised gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst)

---

To me, it looks like there is a "river of stars" flowing along the lower part of the image. Couldn't they be at the same distance from us as Sgr A*?

Ann

[Chris Peterson]

I presume that most (or all?) of those stars are either in the foreground or the background?

Where else could they be?

Perhaps some of them could be at the same distance to us as Sgr A*, to the east or left of Sgr A*?

This composite colour infrared image of the centre of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionised gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst)

---

To me, it looks like there is a "river of stars" flowing along the lower part of the image. Couldn't they be at the same distance from us as Sgr A*?

Ann

The odds of any of them being at the same distance is vanishingly small (actually, impossible). Every star must be either closer to us or farther from us than the black hole!

[Ann]

Where else could they be?

Perhaps some of them could be at the same distance to us as Sgr A*, to the east or left of Sgr A*?

This composite colour infrared image of the centre of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionised gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst)

---

To me, it looks like there is a "river of stars" flowing along the lower part of the image. Couldn't they be at the same distance from us as Sgr A*?

Ann

The odds of any of them being at the same distance is vanishingly small (actually, impossible). Every star must be either closer to us or farther from us than the black hole!

Click to play embedded YouTube video.

Stars orbiting the black hole at the heart of the Milky Way. Time-lapse by ESO.

Are you saying there are no stars in the vicinity of Sgr A*?

Ann

[Chris Peterson]

Perhaps some of them could be at the same distance to us as Sgr A*, to the east or left of Sgr A*?

This composite colour infrared image of the centre of our Milky Way galaxy reveals a new population of massive stars and new details in complex structures in the hot ionised gas swirling around the central 300 light-years. This sweeping panorama is the sharpest infrared picture ever made of the Galactic core. It offers a nearby laboratory for how massive stars form and influence their environment in the often violent nuclear regions of other galaxies. Credit: NASA, ESA and Q.D. Wang (University of Massachusetts, Amherst)

---

To me, it looks like there is a "river of stars" flowing along the lower part of the image. Couldn't they be at the same distance from us as Sgr A*?

Ann

The odds of any of them being at the same distance is vanishingly small (actually, impossible). Every star must be either closer to us or farther from us than the black hole!

Click to play embedded YouTube video.

Stars orbiting the black hole at the heart of the Milky Way. Time-lapse by ESO.

Are you saying there are no stars in the vicinity of Sgr A*?

Ann

Not at all. Only that there are no stars at the same distance. Define "vicinity".

[Ann]

The odds of any of them being at the same distance is vanishingly small (actually, impossible). Every star must be either closer to us or farther from us than the black hole!

Click to play embedded YouTube video.

Stars orbiting the black hole at the heart of the Milky Way. Time-lapse by ESO.

Are you saying there are no stars in the vicinity of Sgr A*?

Ann

Not at all. Only that there are no stars at the same distance. Define "vicinity".

The Milky Way's Black Hole Image Credit: X-ray - NASA/CXC/SAO, IR - NASA/HST/STScI; Inset: Radio - Event Horizon Telescope Collaboration

---

All right, I think I get what you are saying - maybe. The luminous radio disk of the black hole is about the size of the orbit of Mercury, and I guess no stars are found inside it (because if they blunder in there, they will be shredded and then swallowed).

But the larger panel of today's APOD is 7 light-years across, according to today's caption.

You can't possibly say that there are no stars within 7 light-years of the black hole at the center of the Milky Way!

Ann

[Chris Peterson]

Are you saying there are no stars in the vicinity of Sgr A*?

Not at all. Only that there are no stars at the same distance. Define "vicinity".

All right, I think I get what you are saying - maybe. The luminous radio disk of the black hole is about the size of the orbit of Mercury, and I guess no stars are found inside it (because if they blunder in there, they will be shredded and then swallowed).

But the larger panel of today's APOD is 7 light-years across, according to today's caption.

You can't possibly say that there are no stars within 7 light-years of the black hole at the center of the Milky Way!

No. I'm saying that every star in the image is either in the foreground or the background.

(FWIW, the black hole image is 1/100 of one pixel of the larger image!)

[Ann]

Not at all. Only that there are no stars at the same distance. Define "vicinity".

All right, I think I get what you are saying - maybe. The luminous radio disk of the black hole is about the size of the orbit of Mercury, and I guess no stars are found inside it (because if they blunder in there, they will be shredded and then swallowed).

But the larger panel of today's APOD is 7 light-years across, according to today's caption.

You can't possibly say that there are no stars within 7 light-years of the black hole at the center of the Milky Way!

No. I'm saying that every star in the image is either in the foreground or the background.

(FWIW, the black hole image is 1/100 of one pixel of the larger image!)

I certainly realize that the black hole is way, way to small to be visible in the larger image.

But when you say that all the stars seen in the larger image have to be either in the foreground or in the background (and not, say, within a few light-years of the black hole), I frankly don't get it.

Ann

[Chris Peterson]

All right, I think I get what you are saying - maybe. The luminous radio disk of the black hole is about the size of the orbit of Mercury, and I guess no stars are found inside it (because if they blunder in there, they will be shredded and then swallowed).

But the larger panel of today's APOD is 7 light-years across, according to today's caption.

You can't possibly say that there are no stars within 7 light-years of the black hole at the center of the Milky Way!

No. I'm saying that every star in the image is either in the foreground or the background.

(FWIW, the black hole image is 1/100 of one pixel of the larger image!)

I certainly realize that the black hole is way, way to small to be visible in the larger image.

But when you say that all the stars seen in the larger image have to be either in the foreground or in the background (and not, say, within a few light-years of the black hole), I frankly don't get it.

Ann

I fail to see what else they could be. They're either between us and the black hole, or they are behind it. (I didn't say anything about a few light years.)

Perhaps the question was whether any of the stars in the image are orbiting the black hole? The handful of stars that we have observed orbiting Sgr A* range in distance from about 10 AU to about 2000 AU, most being at the lower end of that range. A star 2000 AU from the black hole would be 15 pixels away in the large image. Which would be lost in a region of saturated pixels. So the answer is no, none of the stars in this image are likely to be orbiting Sgr A*, except to the extent that being so close to the center of the galaxy, a few might be nearly orbiting it (while actually orbiting the galaxy's center of mass, which is likely very close to Sgr A*). What is actually orbiting what can be difficult to define clearly in closely interacting multiple body systems.

(I know you're aware that the SMB is too small to be seen. I was just pointing out how incredibly small, at 1% of a single pixel.)

[johnnydeep]

All right, I think I get what you are saying - maybe. The luminous radio disk of the black hole is about the size of the orbit of Mercury, and I guess no stars are found inside it (because if they blunder in there, they will be shredded and then swallowed).

But the larger panel of today's APOD is 7 light-years across, according to today's caption.

You can't possibly say that there are no stars within 7 light-years of the black hole at the center of the Milky Way!

No. I'm saying that every star in the image is either in the foreground or the background.

(FWIW, the black hole image is 1/100 of one pixel of the larger image!)

I certainly realize that the black hole is way, way to small to be visible in the larger image.

But when you say that all the stars seen in the larger image have to be either in the foreground or in the background (and not, say, within a few light-years of the black hole), I frankly don't get it.

Ann

Me neither. Why couldn't there be stars to either side (in the larger image), yet be the same distance from us as the black hole?