Ask Me Anything AMA with Astrophysicist Dr. Joe Pesce!

Status
Not open for further replies.

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960

Hey Astronomy Fans!

I’m happy to be here again on this AMA! Your questions and enthusiasm are great, and I look forward to hanging out with you this week.

To recap my background: 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!!

My knowledge base is broad, but I know most about the areas I mentioned above so might have to do some research to find the answer to areas outside my day-to-day experience. Please be patient with me - the universe is enormous!

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. I will try to answer as many questions as possible.

Astronomy continues to surprise and inspire. Thank you for letting me share it with all of you!

Dr Joe
 
Last edited by a moderator:
Jun 1, 2020
1,321
1,097
3,060
Great to have you back!

There were a few papers last year, one from U of Texas, that used cluster microlensing to see those enigmatic very hi-z distant galaxies. They offered a rough estimate for the number of galaxies in the observable universe -- about 2 trillion.

Is 2 trillion a rough number you would favor at this time? If so, given their early age, what would be a rough number for their average no. of stars within each galaxy? [We are so close to an Avogadro number. :)]

Will we always be highly limited in what we can discover about those microlensed galaxies?
 
Jun 1, 2020
1,321
1,097
3,060
Also, I'm fascinated with the history of astronomy. Do you have an area of history you would like questions? [Just finished a book about the 1919 eclipse and the results of the two teams lead by Dyson and Eddington.]

P.S. How do you rate the newest Star Trek series?
 
Feb 8, 2021
58
24
35
Hey Joe, where you going with that telescope in your hand?....sorry, I couldn't resist- I'm nervous, so many questions so little spacetime...
Ok, first if a BH reached its "density maximum" -soon to be determined, by me hopefully-and collapsed "again" ripping a hole in spacetime and then became a "whitehole" or expansive in energy then its energy would be FTLS(faster than light speed), or inflationary, because a BH can trap light, so its energy is greater than lights speed and if this energy was inverted or became expansive it would be FTLS...this is part of my theory for our universe but not for "the beginning of all universes"...for that theory I have to charge you, I take visa....
 
Jul 4, 2020
8
5
15

Hey Astronomy Fans!

I’m happy to be here again on this AMA! Your questions and enthusiasm are great, and I look forward to hanging out with you this week.

To recap my background: 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!!

My knowledge base is broad, but I know most about the areas I mentioned above so might have to do some research to find the answer to areas outside my day-to-day experience. Please be patient with me - the universe is enormous!

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. I will try to answer as many questions as possible.

Astronomy continues to surprise and inspire. Thank you for letting me share it with all of you!

Dr Joe
 
  • Like
Reactions: jchamot
Jul 4, 2020
8
5
15
Hi Joe
Black holes can hold entire galaxies in form and the speed of gravity is roughly as fast as the speed of electromagnetic waves squared. So could gravity, as one of the four forces in our standard model of particle physics be limited to our universe?
Hey Joe, where you going with that telescope in your hand?....sorry, couldn't I resist- I'm nervous, so many questions so little spacetime...
Ok, first if a BH reached its "density maximum" -soon to be determined, by me hopefully-and collapsed "again" ripping a hole in spacetime and then became a "whitehole" or expansive in energy then its energy would be FTLS(faster than light speed), or inflationary, because a BH can trap light, so its energy is greater than lights speed and if this energy was inverted or became expansive it would be FTLS...this is part of my theory for our universe but not for "the beginning of all universes"...for that theory I have to charge you, I take visa....
 
  • Like
Reactions: jchamot
Sep 22, 2020
8
6
15
Dr. Joe,

It's well known that galactic "dark matter" measurements rest on Newtonian gravity. E.g. galaxy rotation curves are generated based on a Newtonian model of a galaxy spinning in an otherwise empty universe. There have been some grumblings about this lately; Dr. Becky did a podcast on it. It seems almost impossible that these two short-cuts--using Newton's laws in an empty universe--could account for dark matter. Any comments?
 
  • Like
Reactions: jchamot
Feb 8, 2021
58
24
35
Wouldn't a supercluster of galaxies, finding the low gravity point, have all of there BH's merge and this could form a massive BH that would be trillions of solar masses, and the radius and spin would have to cause another collapse eventually in the BH?...just saying...
 
  • Like
Reactions: jchamot

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Great to have you back!

There were a few papers last year, one from U of Texas, that used cluster microlensing to see those enigmatic very hi-z distant galaxies. They offered a rough estimate for the number of galaxies in the observable universe -- about 2 trillion.

Is 2 trillion a rough number you would favor at this time? If so, given their early age, what would be a rough number for their average no. of stars within each galaxy? [We are so close to an Avogadro number. :)]

Will we always be highly limited in what we can discover about those microlensed galaxies?
Thanks, Helio - it's good to be back!

Yeah, isn't this fascinating? Our estimates are going to change as our technology improves and we make new discoveries. I think that's a pretty good number! We are still trying to understand these early galaxies, but I think they are smallish. I'm not sure what an average number of stars is, but probably in the millions.

On the other hand, I'm intrigued by the recent discoveries of galaxies larger than expected early in the universe. See, for example, this based on ALMA observations:

https://www.space.com/old-galaxy-in-early-universe-aless0731

And the James Webb Space Telescope will tell us more!
 

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Also, I'm fascinated with the history of astronomy. Do you have an area of history you would like questions? [Just finished a book about the 1919 eclipse and the results of the two teams lead by Dyson and Eddington.]

P.S. How do you rate the newest Star Trek series?
History of all types (and periods) fascinates me. I'm particularly fond of 16th and 17th century England and the Netherlands (and other places too!), where science as we know it today is getting started.

I love all things Star Trek, including the new series. The top for me is still TOS! :)
 
  • Like
Reactions: jchamot
Jun 23, 2020
39
21
35
Hello, Joe. Welcome back. I have 2 questions: 1.) There is still so much we don’t know about gravity and what propagates its “force”. And the existence of a graviton is still a theory. So, what are your thoughts about the Loop Quantum Gravity (LQG) theories? I’m currently reading a book by Jim Baggott titled “ Quantum Space: Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe.”

2.) Do you think we are done with adding to the Standard Model of Particle Physics? Or will theoretical physicists keep looking for smaller and smaller particles?
 
  • Like
Reactions: jchamot
Feb 8, 2021
58
24
35
I just remembered that stars of a certain size collapse to a BH so...BH's of a certain size must also "collapse again" and would this pertain to the permittivity/permeability of space constant, or break it?...
 
  • Like
Reactions: jchamot
Jun 23, 2020
39
21
35
Thanks, Helio - it's good to be back!

Yeah, isn't this fascinating? Our estimates are going to change as our technology improves and we make new discoveries. I think that's a pretty good number! We are still trying to understand these early galaxies, but I think they are smallish. I'm not sure what an average number of stars is, but probably in the millions.

On the other hand, I'm intrigued by the recent discoveries of galaxies larger than expected early in the universe. See, for example, this based on ALMA observations:

https://www.space.com/old-galaxy-in-early-universe-aless0731

And the James Webb Space Telescope will tell us more!
Joe, do you know why it is taking so long to get the James Webb Telescope up into space? I’ve been hearing about it for several years.
 
  • Like
Reactions: jchamot

Wolfshadw

Moderator
Apr 1, 2020
409
354
1,060
As a fellow ST:TOS fan, I was wondering how you feel about the "remastered"version of episodes vs the originals. Have to say that my favorite episode, "The Doomsday Machine" felt a lot cooler/smoother than the original version.

-Wolf sends
 
  • Like
Reactions: jchamot

Wolfshadw

Moderator
Apr 1, 2020
409
354
1,060
I would also note this member's question:

@Artistscientist asks:
Dr. Pesce,
How do we know the Red Shift that we view isn't caused by some unknown physical property of the universe that we cannot see or detect? I feel that the ancient textbook answer of the Doppler effect was too easy, especially considering how much Dark Matter mass we are not taking into account very well, and the unknown quantum effects at great distance. Who are the astrophysicists that are writing about another reason for the Red Shift? Thank you.
Best, Doug Czor
Wolfshadw
Moderator
 
  • Like
Reactions: jchamot and rabsal

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Hi Joe
Black holes can hold entire galaxies in form and the speed of gravity is roughly as fast as the speed of electromagnetic waves squared. So could gravity, as one of the four forces in our standard model of particle physics be limited to our universe?
Supermassive black holes are indeed big, but not compared to the entire galaxy in which they are found. For example, a 5 or 6 billion solar mass black hole may be in a galaxy with a trillion solar masses of stars and stuff. So, they are there, but they aren't affecting (significantly) the rest of the galaxy via their mass, at least. We think the mass of the black hole is related to the mass of the galaxy (high mass black hole in high mass galaxy), and this is a hint of some feedback, not yet understood. Maybe in the early days of the galaxy formation the black hole played a bigger role.

Of course, we only know of one universe, so I can't comment on the forces. And, as far as we can tell, gravitational waves travel at the speed of light.
 
  • Like
Reactions: jchamot

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Dr. Joe,

It's well known that galactic "dark matter" measurements rest on Newtonian gravity. E.g. galaxy rotation curves are generated based on a Newtonian model of a galaxy spinning in an otherwise empty universe. There have been some grumblings about this lately; Dr. Becky did a podcast on it. It seems almost impossible that these two short-cuts--using Newton's laws in an empty universe--could account for dark matter. Any comments?
Some measurements are based on Newtonian dynamics (coupled with Kepler's laws), the rotation curves you mention. There are other ways to measure the presence of dark matter - gravitational lensing, for example. I'm not aware of the podcast and would have to view that before I can comment. There are alternative models, of course; mostly because the dark matter particle hasn't yet been identified.
 
  • Like
Reactions: jchamot

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Wouldn't a supercluster of galaxies, finding the low gravity point, have all of there BH's merge and this could form a massive BH that would be trillions of solar masses, and the radius and spin would have to cause another collapse eventually in the BH?...just saying...
In a super cluster - or even more so in a rich cluster of galaxies - there is usually a big "giant elliptical galaxy" sitting near the bottom of the gravitational potential well. And you are correct, the other, smaller, galaxies are falling in, and they will eventually merge, adding their stars/gas to and increasing the mass of, the central giant elliptical galaxy. Any central supermassive black hole will likely merge with the supermassive black hole in the central galaxy as well, and the result will be a larger black hole.

Remember, though, as I said in another response, the central supermassive black holes may only be 1% the mass of their host galaxies. A rich cluster of galaxies might have, say, 1,000 galaxies. IF they all coalesce into the central cluster galaxy (they probably won't) and IF they all had a 1 billion solar mass black hole (a guess), then the resulting supermassive black hole would be around 1 trillion solar masses. Again, though, this is an extreme case - the central super massive black holes probably wouldn't get that large (at least in the current age of the universe).
-----
 
  • Like
Reactions: jchamot
Mar 27, 2020
4
4
515
As a fellow ST:TOS fan, I was wondering how you feel about the "remastered"version of episodes vs the originals. Have to say that my favorite episode, "The Doomsday Machine" felt a lot cooler/smoother than the original version.

-Wolf sends
This is such a great question... is it possible to love both? The remaster is stunning, but from time to time, it's just fun (and authentic) to watch the original effects...with the Doomsday Machine looking so much like a cannoli being one of them, yet benefitting so much from the upgrade...
 
Jul 4, 2020
8
5
15
Th
Supermassive black holes are indeed big, but not compared to the entire galaxy in which they are found. For example, a 5 or 6 billion solar mass black hole may be in a galaxy with a trillion solar masses of stars and stuff. So, they are there, but they aren't affecting (significantly) the rest of the galaxy via their mass, at least. We think the mass of the black hole is related to the mass of the galaxy (high mass black hole in high mass galaxy), and this is a hint of some feedback, not yet understood. Maybe in the early days of the galaxy formation the black hole played a bigger role.

Of course, we only know of one universe, so I can't comment on the forces. And, as far as we can tell, gravitational waves travel at the speed of light.
Thank you! I believe gravitational waves are electromagnetic.
 
  • Like
Reactions: jchamot
Feb 8, 2021
58
24
35
In a super cluster - or even more so in a rich cluster of galaxies - there is usually a big "giant elliptical galaxy" sitting near the bottom of the gravitational potential well. And you are correct, the other, smaller, galaxies are falling in, and they will eventually merge, adding their stars/gas to and increasing the mass of, the central giant elliptical galaxy. Any central supermassive black hole will likely merge with the supermassive black hole in the central galaxy as well, and the result will be a larger black hole.

Remember, though, as I said in another response, the central supermassive black holes may only be 1% the mass of their host galaxies. A rich cluster of galaxies might have, say, 1,000 galaxies. IF they all coalesce into the central cluster galaxy (they probably won't) and IF they all had a 1 billion solar mass black hole (a guess), then the resulting supermassive black hole would be around 1 trillion solar masses. Again, though, this is an extreme case - the central super massive black holes probably wouldn't get that large (at least in the current age of the universe).
-----
Thanks for that but what if dark energy/matter is a liquid plasma that helps form the gravity wells of the superclusters, could that account for even bigger BH's? I think dark energy is a FTLS liquid plasma that our visible universe is expanding into at a slower but increasing rate...inflation proceeded the BB and we are expanding into that....
But even if a supercluster or two got sucked up by BH and collapsed forming an expansion...that is still so small compared to our visible universe expansion(not to say invisible expansion) that even I am having a hard time imagining it...although it would start bigger than what is usually considered for the beginning of the big bang singularity.
 
  • Like
Reactions: jchamot
May 1, 2021
44
34
60
I don't want to pose a question that can't be answered, but I have wondered for a long time whether or not our universe is everything in existence, including all the dimensions we have yet to discover. If this is true, I don't see the universe simply reversing course because it apparently is still accelerating. What I see is a space-time fabric possibly being stretched to its limits before quantum leaping into something with different properties and different laws of physics. From there, it may undergo more quantum leaps before reverting back to whatever it was before the Big Bang.

If the universe is only a fraction of everything in existence, it becomes a much more complicated picture, perhaps beyond the reach of the most intelligent beings to have ever existed. I realize there is a 0.0000000000001% chance we are the only intelligent beings to ever exist in the universe.

Oh, I loved you in "My Cousin Vinny." Just kidding. His surname is Pesci.
 
  • Like
Reactions: jchamot

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
Hello, Joe. Welcome back. I have 2 questions: 1.) There is still so much we don’t know about gravity and what propagates its “force”. And the existence of a graviton is still a theory. So, what are your thoughts about the Loop Quantum Gravity (LQG) theories? I’m currently reading a book by Jim Baggott titled “ Quantum Space: Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe.”

2.) Do you think we are done with adding to the Standard Model of Particle Physics? Or will theoretical physicists keep looking for smaller and smaller particles?
Thank you!

These are great questions, both outside my expertise. So, just some thoughts:

1) The detection of gravitational waves by the NSF's Laser Interferometry Gravitational Wave Observatory (https://www.nsf.gov/news/news_summ.jsp?cntn_id=137628&org=NSF) opened a new vista on the universe. Not only are we making remarkable discoveries about the objects that cause the gravitational waves (https://www.nsf.gov/news/news_summ.jsp?cntn_id=243382), but also about gravitational waves themselves (and, obviously, gravity). I will be looking forward to more information about all the above over the next years as observations continue, and the field advances.

2) I think new astrophysical and particle physics observations/experiments will continue to cause the Standard Model to be tweaked. The model is quite resilient.
 

DrJoePesce

Verified Expert
Mar 31, 2020
117
277
960
I just remembered that stars of a certain size collapse to a BH so...BH's of a certain size must also "collapse again" and would this pertain to the permittivity/permeability of space constant, or break it?...
Yes, the mass of the collapsing star (primarily) will lead to the complete collapse to a singularity. I'm not sure how a black hole can collapse further/again, as the singularity is the ultimate collapsed object.
 
  • Like
Reactions: jchamot
Status
Not open for further replies.

ASK THE COMMUNITY