Ask Me Anything AMA with Dr. Joe Pesce

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DrJoePesce

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Mar 31, 2020
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Hello Everyone.

I’m looking forward to this AMA and to hearing from you with your questions about astronomy! I will try to answer as many as possible.

I'm an astrophysicist primarily interested in the environments of the galaxies hosting supermassive black holes (also known as Active Galactic Nuclei). I've worked with clusters of galaxies, and the atmospheres of giant and supergiant stars. Currently I'm a Program Director at the National Science Foundation (NSF), Division of Astronomical Sciences, responsible for the National Radio Astronomy Observatory (NRAO); a part-time Professor at George Mason University in Fairfax, Virginia; and a Visiting Professor at the University of Colorado, Boulder, Colorado. And I'm a Fellow of the Royal Astronomical Society. Oh - and I LOVE all things Star Trek!!

I have a broad understanding of the field, but it’s vast (one could even say “astronomically” large), so I might need some time to find the answer.

Also, there may be lots of questions I can’t answer, because I don’t know – and maybe the answer isn’t yet known (that’s a fun part about astronomy – lots of unknowns still). Please keep this in mind.

Astronomy is exciting, and we live in an exciting time for the field. Thank you for letting me share it with all of you!

Dr Joe


 
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Aug 22, 2019
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Welcome to our forums! I have a few questions I've been saving up from users (and from myself).

Q. If a black hole is basically just a hyper-concentration of gravity, and a star is a concentrated ball of energy, is there any point at which a black hole can get "filled up"? If so, how many stars would it take to fill one? Or, does the act of "filling" a black hole make it even bigger?

Q. What happens if the beam from a pulsar comes within the event horizon of a black hole? Would it bend the beam which would then continue off into space, or would it circle the drain like light?

Q. Are there any interstellar objects composed of dark matter?

-JP
 

shaines

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Aug 22, 2019
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Hey there,

Thanks for taking the time to hang out with us! I have some questions.

  • Was there any "eureka" moment for you when you decided that astrophysics was your passion?
  • Do you feel confident that we have a good understanding of dark matter and we're just waiting to fill in some blanks, or that we may come to find that we'll need to start from scratch to better understand the processes driving the universe outward?
  • Based on your years of experience in the field, how likely do you think a multiverse is? Is there a mirror version of this universe where we're all there as well, but with goatees and bad intentions? If I have a goatee here, is my alternate version just a clean faced guy who's a real jerk? What if I'm a jerk? Would the alternate be some real cool cat?
 
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Jun 1, 2020
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Howdy! It's a treat to visit with you, so thanks.

1) Do the more massive galaxies typically, perhaps always, have a higher ratio of DM (dark matter) to normal matter compared to smaller galaxies?

2) Do Active Galaxies demonstrate greater metallicity as one gets closer to the "juicy center of the Tootsie Pop" (from Spielberg's Ready Player One)?

3) Any insight to how you hope gravity wave detections will help you and others?
 
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DrJoePesce

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Mar 31, 2020
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Welcome to our forums! I have a few questions I've been saving up from users (and from myself).

Q. If a black hole is basically just a hyper-concentration of gravity, and a star is a concentrated ball of energy, is there any point at which a black hole can get "filled up"? If so, how many stars would it take to fill one? Or, does the act of "filling" a black hole make it even bigger?

Q. What happens if the beam from a pulsar comes within the event horizon of a black hole? Would it bend the beam which would then continue off into space, or would it circle the drain like light?

Q. Are there any interstellar objects composed of dark matter?

-JP
Thanks for the questions!

A1. A black hole is a “singularity” surrounded by an event horizon. The singularity has zero radius, but the event horizon has a finite size (proportional to the mass within it). We do not (cannot?) know what happens to matter and radiation once it is inside the event horizon, so anything about that is pure speculation. Having said that, when matter falls through the event horizon, the mass of the black hole increases (as does the radius of the event horizon). To date, we have observed some very massive black holes: For example, the supermassive black hole in the galaxy M87 is about 6.5 BILLION times the mass of the sun.

A2. If a pulsar beam (which is light) comes within an event horizon, the photons will be absorbed by the black hole. If the beam comes very close to – but outside – of the event horizon , it will indeed bend. The amount of bending depends on how close, but you could get a situation where the photons will go in orbit around the black hole.

A3. Dark matter is everywhere, and surrounds galaxies (made up of normal matter), for example. There could be clouds composed only of dark matter, but I don’t believe we have detected, definitively, such objects
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Hey there,

Thanks for taking the time to hang out with us! I have some questions.

  • Was there any "eureka" moment for you when you decided that astrophysics was your passion?
  • Do you feel confident that we have a good understanding of dark matter and we're just waiting to fill in some blanks, or that we may come to find that we'll need to start from scratch to better understand the processes driving the universe outward?
  • Based on your years of experience in the field, how likely do you think a multiverse is? Is there a mirror version of this universe where we're all there as well, but with goatees and bad intentions? If I have a goatee here, is my alternate version just a clean faced guy who's a real jerk? What's if I'm a jerk? Would the alternate be some real cool cat?
Great questions!

I’ve been interested in astronomy almost my entire life: I read an astronomy-related book, probably when I was about 5 years old and was hooked. (this is quite common among astronomers, by the way). Star Trek (TOS) played a big influence on me, in general, and becoming an astronomer in particular.

I feel confident dark matter exists. Do we truly understand it? There’s a lot of understanding left to do, but we are certainly learning more and more every day. I think the area that might cause us to rethink our understanding of laws of physics is when we finally determine what sort of thing dark matter is (for example, what sort of sub-atomic particle dark matter is).

The multiverse is certainly an intriguing idea. And could be a possibility (including all those things you mention). Many aspects of the multiverse can’t yet be tested, so it remains in the realm of science fiction; but that will change with time. I hope you aren't a jerk in any universe! Cool cat is much better!
 
Jun 23, 2020
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This is super cool, thanks for being here!

Regarding black holes... should we be worried about them, here on planet Earth? My daughter is semi-concerned that we'll get sucked up into one eventually, haha.
 
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Jun 23, 2020
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I'm a huge fan of The Expanse, a sci-fi and television series that takes place in a near future where earthlings have colonized the solar system. Have you heard of it?

In the latest season, humans have discovered an intergalactic super highway. The highway is comprised of thousands of wormhole gates, called "rings". These rings are essentially wormhole tunnels that allow for interstellar travel between our solar system and the rest of the galaxy.

I have three questions:

- Do you think a wormhole network is the only way interstellar travel will ever be possible?

- What kind of technology be at the foundation of this wormhole super highway? I

- Is there anything we are working on now that will lead to this technology?

Thanks!
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Howdy! It's a treat to visit with you, so thanks.

1) Do the more massive galaxies typically, perhaps always, have a higher ratio of DM (dark matter) to normal matter compared to smaller galaxies?

2) Do Active Galaxies demonstrate greater metallicity as one gets closer to the "juicy center of the Tootsie Pop" (from Spielberg's Ready Player One)?

3) Any insight to how you hope gravity wave detections will help you and others?
It's a treat for me too to visit with you!

So, here we go!

1) I’m not sure about always, but it does appear more massive galaxies have more dark matter compared to smaller galaxies. Why? Don’t know, but a question is which came first, the DM or the galaxy? And more observations will help us understand this fundamental question.

2) I like Tootsie Pops – one, two, thareee… (get it! :cool: ). Ah, sorry, got distracted.
I’m not aware of any studies that show changing metallicity as one gets closer to the nucleus. So just to add some context: Active galaxies (or, Active Galactic Nuclei – AGN, to give their full name) have a supermassive, feeding, black hole in their centers (their nuclei). Metallicity refers to how many heavy elements are present in a gas (for astrophysicists, “heavy element” means elements heavier than helium). All such elements are created in the fusion reactions in the centers of massive stars, or in thei explosions as a supernova (there are some other sources…). The first generation of stars was formed out of material from the big bang, so hydrogen (mostly) and helium only. After that first generation, heavier elements started to “pollute” the gas clouds from which later generations of stars formed, and so the metallicity increases. For this question, I suppose there could be unusual star formation near the active nucleus, but that’s probably not a big deal. Rather, studies seem to indicate that there is a connection between metallicity in the galaxy and any active nucleus, maybe indicating that galaxy mass (and star formation) is the important factor in causing the nuclear activity.

3) Gravitational waves give us a new “window” on the universe, and as such, allow us to study new objects we didn’t previously know exist, and learn about old friends in a new way. So, yes, gravitational wave detections will be a most useful tool! And, while we are on the topic, here is a cool new result from NSF's LIGO (Laser Interferometer Gravitational-Wave Observatory):

https://www.ligo.caltech.edu/news/ligo20200623?highlight=GW190814
 
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sward

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From Hecktor on twitter:

"I have read around reports on how low the solar activity has been and how good that is for astronauts and science. It that because of the supposedly Solar Cycle 25 that had begun? "
 
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DrJoePesce

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Mar 31, 2020
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This is super cool, thanks for being here!

Regarding black holes... should we be worried about them, here on planet Earth? My daughter is semi-concerned that we'll get sucked up into one eventually, haha.
Thanks for participating CleverGirl!

Neither your daughter nor you (nor anyone else!) should worry: Even though black holes can have a lot of mass, their size is (relatively) small. For example, if I could make our sun magically turn into a black hole, the event horizon would have a radius of only about 2 miles. [NOTE: The sun can NOT turn into a black hole. I was using my magical astrophysicist wand (also called imagination) to do this.] Even the supermassive black holes in the centers of galaxies – millions to billions of times the mass of our sun – are only about the size of our solar system (big for humans, tiny for the universe).

By the way, the nearest stellar-sized black so far detected is about 1,000 light years away. The nearest supermassive one is in the center of our galaxy, about 26,000 light years away.

So we are probably safe from being sucked into a black hole....

I hope you daughter's interest means she will become a black hole expert and make the next big discoveries in the field!
 

DrJoePesce

Verified Expert
Mar 31, 2020
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I'm a huge fan of The Expanse, a sci-fi and television series that takes place in a near future where earthlings have colonized the solar system. Have you heard of it?

In the latest season, humans have discovered an intergalactic super highway. The highway is comprised of thousands of wormhole gates, called "rings". These rings are essentially wormhole tunnels that allow for interstellar travel between our solar system and the rest of the galaxy.

I have three questions:

- Do you think a wormhole network is the only way interstellar travel will ever be possible?

- What kind of technology be at the foundation of this wormhole super highway? I

- Is there anything we are working on now that will lead to this technology?

Thanks!
Keep up the SF interest!

Wormholes. Predicted by Einstein, but not yet detected (hmmm, is this the only thing predicted by Einstein but not yet proven to exist? Maybe…). Certainly, worm holes are the foundation of lots of SF stories, where we can play and speculate. If wormholes work as they are depicted in SF, then they are a great way to travel large distances. And traveling large distances is the key, as even for the shortest trips (to the nearest star, say), the distances are astronomical.

I would love for wormholes to exist – and to be able to use them as superhighways – but we will have to wait and see. The short answer to your question about anyone working on technology is probably no. But all basic research (for example in physics and astrophysics – the sort of research we fund at the NSF) informs our understanding of the universe around us, advances technology, and makes future technology (that we can’t even imagine today) possible. So, in this sense, the answer is yes!
 

DrJoePesce

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Mar 31, 2020
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From Hecktor on twitter:

"I have read around reports on how low the solar activity has been and how good that is for astronauts and science. It that because of the supposedly Solar Cycle 25 that had begun? "
Welcome Hecktor!

Solar activity has indeed by low, but we have also been in the minimum of the latest solar cycle (which is about 11-years long). We are now starting to come out of the minimum, so could expect solar activity to increase over the next several years.

Low solar activity is good for astronauts because when the sun is active, it can produce things like flares (violent releases of high energy photons, like x-rays), and “coronal mass ejections” (violent releases of huge amounts of charged parcticles – electrons and protons). If either of these explosions are pointed toward earth/astronauts, the electromagnetic radiation and high-energy charged particles can cause lots of problems. This is one reason why long-duration space travel (even to Mars, for example), is problematic: It’s very difficult – and expensive – to shield and protect humans.

By the way, have you seen the first light image from our latest observatory, the NSF's Daniel K Inoue Solar Telescope (DKIST). This is the highest-resolution image of the sun ever taken.

https://www.nso.edu/inouye-solar-telescope-first-light/
 
Apr 5, 2020
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I am very happy to have an expert in the Space.com Forums! I have some questions. Please answer them.

Q-1 How come black holes are possible? I mean, how can mass be there where there is no space as there cannot be any particle without space?

Q-2 What do you think about Relativity? Have we got enough evidence to prove it wrong?

I will be very happy if you answer them!
 
Jun 23, 2020
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Hello Dr. Pesce

My question is about black holes. I have read about the hawing radiation and that with time black holes discipate but what if a black holes keeps feeding non stop or even merging with other super massive black holes. Is there any limit in which the matter will transform into something else maybe a singularity?. How much mass you would need for that to happen?. With the current understanding of physics is this something we can calculate?
 
Aug 22, 2019
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Having said that, when matter falls through the event horizon, the mass of the black hole increases (as does the radius of the event horizon)
Have we, to date, witnessed a perceivable increase in the mass of a black hole due to matter falling into it? And, if this is the case, and black holes simply get larger and larger as they consume matter, doesn't that mean that eventually the universe will simply collapse into one super-massive black hole?

If a pulsar beam (which is light) comes within an event horizon, the photons will be absorbed by the black hole. If the beam comes very close to – but outside – of the event horizon , it will indeed bend. The amount of bending depends on how close, but you could get a situation where the photons will go in orbit around the black hole.
So if you had a couple small black holes in orbit around a pulsar that you could fine tune positioning on, you could, you could theoretically use them to "aim" the pulsar beam? Not that any sane person would want to do that, of course.

Come to think of it, does anything actually cause a black hole to move?
 

DrJoePesce

Verified Expert
Mar 31, 2020
88
229
410
I am very happy to have an expert in the Space.com Forums! I have some questions. Please answer them.

Q-1 How come black holes are possible? I mean, how can mass be there where there is no space as there cannot be any particle without space?

Q-2 What do you think about Relativity? Have we got enough evidence to prove it wrong?

I will be very happy if you answer them!

Thank you!

This is a story about gravity. Gravity is an attractive force that operates on objects with mass. Gravity’s “goal”, if you will, is to crush things out of existence. If there is enough mass, and with a violent, energetic, event (such as explosion of a massive star), gravity can win and crush the mass of the core of the star “out of existence” – into a black hole. The singularity has zero radius but contains the mass of the object that was crushed. This means the gravitational field is immense, so strong that not even light can escape. Certainly, the laws of physics break down at the singularity (fundamentally because it has zero radius, but many physical laws have a radius term in them. So, when radius is zero, those equations don’t “work” anymore). It’s for this reason (primarily) that we can’t understand what happens inside the event horizon of a black hole.

Relativity is great! Such an insightful mind Einstein had. No evidence has been found to prove it wrong: Every test of relativity to date has failed to invalidate it
 
Apr 5, 2020
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Thank you for your answers! I have some more questions.

Q-1: Is the Anthropic Principle right? If so, please state your statements that support it. If not, then please state your statements that do not support it.
Q-2: Can we make an artificial black hole? Is it possible yet? Is it possible in the future?
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Have we, to date, witnessed a perceivable increase in the mass of a black hole due to matter falling into it? And, if this is the case, and black holes simply get larger and larger as they consume matter, doesn't that mean that eventually the universe will simply collapse into one super-massive black hole?
Black holes generally "feed" slowly (in a relative sense) such that the added mass is a small percentage of the total mass. This is true for a stellar-sized black hole (say with 5 times the mass of the sun) pulling mass from a nearby companion star, or a supermassive black hole (say with 1 billion times the mass of the sun) consuming a star with 2-3 solar masses. If we had sensitive enough instruments we could measure that change, but I don't believe we are quite there yet.

The universe is expanding, meaning stuff is getting farther away from other stuff, so probably the whole universe collapsing into a black hole is not possible.

As for the really big black holes - say the one in M87 with 6.5 billion solar masses: That's a LOT of mass. But the galaxy in which that big black hole is found has trillions of solar masses in gas, dust, stars, dark matter. So the black hole is big - but it's minuscule compared to the rest of the galaxy.

So if you had a couple small black holes in orbit around a pulsar that you could fine tune positioning on, you could, you could theoretically use them to "aim" the pulsar beam? Not that any sane person would want to do that, of course.
You could, I suppose, but they would be orbiting each other so that would really complicate any aiming. If you had the capability of doing that, frankly, I think it would be easier just to torque the entire pulsar around to whatever direction you had in mind....

Come to think of it, does anything actually cause a black hole to move?
Sure, black holes are masses so they are affected by other masses (and hence gravity) around them. Small black holes in the galaxy orbit around the galaxy just like the stars, they orbit companions, they fall into the centers of galaxies, etc.
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Hello Dr. Pesce

My question is about black holes. I have read about the hawing radiation and that with time black holes discipate but what if a black holes keeps feeding non stop or even merging with other super massive black holes. Is there any limit in which the matter will transform into something else maybe a singularity?. How much mass you would need for that to happen?. With the current understanding of physics is this something we can calculate?

If I understand your question Azrael, you are asking if black holes can lose mass/energy through hawking radiation (and, potentially, evaporate), what happens if they continue feeding?

Hawking radiation is a mechanism whereby a black hole can lose mass/energy. But through hawking radiation, the black hole loses very small amounts mass/energy very slowly. It would take an immense amount of time for even a black hole with the mass of our sun to evaporate (far longer than the current age of the universe). If a black hole is feeding every once-in-awhile, that extra mass far outweighs the loss of mass by hawking radiation.
 
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Jun 1, 2020
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Ironies add flavor to many facts...

Since a person could go unharmed in passing across the EH (Event Horizon) of a SMBH but become "spaghettified" if it were a smaller one, do you happen to know what the cut-off point (pun intended ;)) in mass would be between the two?
 
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