Ask Me Anything Dr Joe AMA

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DrJoePesce

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Mar 31, 2020
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Hey Astronomy Fans!

Happy 2022! Our previous AMA sessions have been a blast, and I hope you agree. Lots of things going on in the universe and I'm back to share them with you.

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 Officer 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.

Not a day goes by that something amazing is revealed to us about astronomy. Thank you for letting me share it with all of you!

Dr Joe
 

COLGeek

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Apr 3, 2020
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Dr. Joe,

What are your expectations/desires for the first images from the JWST? Are you excited for the new insights into our understanding of the universe?

COLGeek
 
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Howdy Joe, nice to see you back!

The JWST is such huge news right now so, as a radio astronomer, do you expect radio astronomers to be especially interested in the JWST's results, given their observations are closer in wavelengths than optical work?
 
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IG2007

"Don't criticize what you can't understand..."
Apr 5, 2020
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Hey there, Joe, glad to have you back!

What do you think is the most important work of the JWST? And, regarding your area of expertise, how do you think supermassive blackholes form? Can they have any similarities to primordial blackholes?
 

DrJoePesce

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Dr. Joe,

What are your expectations/desires for the first images from the JWST? Are you excited for the new insights into our understanding of the universe?

COLGeek

Hi COLGeek - thanks for the question! Bottom line is that JWST is going to give us great insight into almost all areas of astrophysics we are currently following: star formation, galaxies and galaxy formation, black holes, early universe. I love it all, of course, but given some recent observations from very early in the universe, I think I'm most excited to see what JWST can provide to us on that topic. But, of course, the most exciting thing is what we AREN'T expecting - and those sorts of discoveries are made every day and in particular when new instruments come online!
 

DrJoePesce

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Howdy Joe, nice to see you back!

The JWST is such huge news right now so, as a radio astronomer, do you expect radio astronomers to be especially interested in the JWST's results, given their observations are closer in wavelengths than optical work?

Hi Helio - it's nice to be back! The short answer is yes, for the reason you give, but also because observations in multiple wavelengths are always complementary. Astronomical objects are not emitting in just one wavelength at a time, so by studying them across the electromagnetic spectrum we gain a better understanding of them and the physics that is driving them.
 
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DrJoePesce

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Hey there, Joe, glad to have you back!

What do you think is the most important work of the JWST? And, regarding your area of expertise, how do you think supermassive blackholes form? Can they have any similarities to primordial blackholes?

Thanks IG2007! Lot's of JWST questions, understandably! In my opinion, the most important observations coming from JWST will be early universe stuff (which, yes, will be about the first stars, galaxy and supermassive black hole formation, etc.), and, again, everything that we don't expect or anticipate right now. We may detect primordial blackholes, but I think the insight we could gain from the "run-of-the-mill" supermassive ones will be remarkable.

By the way, here are some (weird and unexpected) results from the early universe. JWST will provide more of this, and hopefully some clarity:




 
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Hi Helio - it's nice to be back! The short answer is yes, for the reason you give, but also because observations in multiple wavelengths are always complementary. Astronomical objects are not emitting in just one wavelength at a time, so by studying them across the electromagnetic spectrum we gain a better understanding of them and the physics that is driving them.
Yes, thanks. But I was wondering if there were any, more unique nuances that cross over in these two broad bands. Do you know off-hand, for instance, if there are absorption lines of a given element or molecule in the IR that also are complimentary to radar, but not in the optical?

Also, could the high power radio or microwave transmission to, say, a cold near earth asteroid produce enough heating for the JWST to detect the increase?
 
Jun 1, 2020
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Yes, thanks. But I was wondering if there were any, more unique nuances that cross over in these two broad bands. Do you know off-hand, for instance, if there are absorption lines of a given element or molecule in the IR that also are complimentary to radar, but not in the optical?

Also, could the high power radio or microwave transmission to, say, a cold near earth asteroid produce enough heating for the JWST to detect the increase? [Perhaps lasers would be better, I suppose.]
 
Mar 21, 2021
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Dr. Joe,

I really appreciate you taking the time to answer questions such as this. Here are a few questions on my mind:

I understand that studies have shown that there are galaxies without, or with very little, dark matter. How does not having dark matter affect galaxy formation? Are these galaxies far more diffuse?

Do you believe that supermassive black holes explain some of the phenomenon that we are attributing to dark matter? Is there any theorized relationship between black holes and dark matter? Is it your belief that, since dark matter interacts with gravity, that much, and maybe most, of the matter creating black holes came from dark matter? How does that affect your understanding of black hole formation?

Do the current theories on the formation of the universe starting with the big bang account for the potential of dark matter, of does this leave a serious theoretical hole in our current interpretation of the Big Bang?

Well, dozens more questions, but I'd better stop there!
 
Apr 5, 2021
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Hi

I was wondering if cryogenic fuels such as being used on SpaceX Starship are safe to be for landings on Earth as compared to kerosin fuels? I have a feeling their flammability present is to great of a risk, in the lower atmosphere. Can the kerosin be used there instead whilst using cryo fuel in takeoff and stratosphere only?

Thanks
 
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Nov 3, 2021
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Hi Dr. Joe Pesce! Thank you very much for spending some time here!

I'm currently studying maths and physics to head to university and study astrophysics! My dream job is to be a starchaser - a little on the nose I know but who says we can't have fun right!

Today I had the realisation that gravity is a true constant. From what I can deduct all other forces can be turned on or off, e.g. heat, light, kinetic energy.... Why does energy have this force? And are there any other forces that are constantly outputting?
 
Mar 30, 2020
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Hi Dr. Joe! I'm definitely not a scientist, but really appreciate the ability to anonymously ask what is probably a dumb question...

When looking at the Bell that is often used to show the size of the universe it is always so hard for me to conceive of something expanding that fast. Then I wondered if the times given are relative to someone in the universe rather then an externa observer. So inflation seemed to take 10 -32 s but that is just because the universe was expanding at near light speed so time would be non existent from within the universe where as if someone was to observe it externally is really could of taken the the 380.000 years and is represented in the Cosmic Microwave Background?
 

DrJoePesce

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Helio - yes, definitely cold gas with molecules producing spectral lines might only be visible in radio or Infrared (IR) (by the way, you say "radar" in the first paragraph, but I know you mean "radio"). It might not be that molecules aren't producing spectral lines in the visible parts of the electromagnetic spectrum (and they do), but that targets of an ALMA observation (say gas 20-30 degrees above absolute zero) or JWST are more strongly emitting in the radio/IR.

Here's an example of the power of a telescope observing where molecules emit strongly:

https://public.nrao.edu/gallery/spectral-lines-in-the-cats-paw-nebula/

As for the 2nd question: I'm not a JWST expert, but I would think that is not possible (or unlikely).
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Dr. Joe,

I really appreciate you taking the time to answer questions such as this. Here are a few questions on my mind:

I understand that studies have shown that there are galaxies without, or with very little, dark matter. How does not having dark matter affect galaxy formation? Are these galaxies far more diffuse?

Do you believe that supermassive black holes explain some of the phenomenon that we are attributing to dark matter? Is there any theorized relationship between black holes and dark matter? Is it your belief that, since dark matter interacts with gravity, that much, and maybe most, of the matter creating black holes came from dark matter? How does that affect your understanding of black hole formation?

Do the current theories on the formation of the universe starting with the big bang account for the potential of dark matter, of does this leave a serious theoretical hole in our current interpretation of the Big Bang?

Well, dozens more questions, but I'd better stop there!

Thanks Epiphany - great questions! In some cases, follow-up observations of a particular galaxy without dark matter have shown that it is, in fact, present.

I think a galaxy without dark matter is still possible - it might be smaller or more compact than we typically see galaxies to be. Remember, dark matter is just like ordinary matter - from the gravitational perspective. So, stars' orbits will be affected the more dark matter there is (just as if there were more ordinary matter).

I don't think supermassive black holes (or even smaller ones) are related to dark matter. Forty years ago (or so) they were dark matter candidates, but the current thinking is that there are not enough of them to produce what we observe. Dark matter could certainly be within black holes. Not sure how dark matter really bas affected their formation and growth. Although, the fact that we are seeing really big black holes very early in the universe might be an indication that dark matter is at play there.

We don't yet know what dark matter is, so we need to understand that before we can say for certain how that might affect the Big Bang model. But I think it's safe to say that current candidates for dark matter are not at odds with our understanding of the Big Bang.

There's a nice, new, article on dark matter here:

https://www.space.com/20930-dark-matter.html

Keep the questions coming!
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Hi

I was wondering if cryogenic fuels such as being used on SpaceX Starship are safe to be for landings on Earth as compared to kerosin fuels? I have a feeling their flammability present is to great of a risk, in the lower atmosphere. Can the kerosin be used there instead whilst using cryo fuel in takeoff and stratosphere only?

Thanks
I'm sorry suneritz, this is outside my area of expertise.
 

DrJoePesce

Verified Expert
Mar 31, 2020
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414
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Hi Dr. Joe! I'm definitely not a scientist, but really appreciate the ability to anonymously ask what is probably a dumb question...

When looking at the Bell that is often used to show the size of the universe it is always so hard for me to conceive of something expanding that fast. Then I wondered if the times given are relative to someone in the universe rather then an externa observer. So inflation seemed to take 10 -32 s but that is just because the universe was expanding at near light speed so time would be non existent from within the universe where as if someone was to observe it externally is really could of taken the the 380.000 years and is represented in the Cosmic Microwave Background?
Hi ITNinja - no questions are dumb! Those times are real times in the history of the universe. In fact, expansion can be faster than the speed of light (and would have been in the inflationary period you mention: between 10^-36 seconds and about 10^-32 seconds).

Have I answered your question? Feel free to follow-up if not!
 

DrJoePesce

Verified Expert
Mar 31, 2020
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414
1,960
Hi Dr. Joe Pesce! Thank you very much for spending some time here!

I'm currently studying maths and physics to head to university and study astrophysics! My dream job is to be a starchaser - a little on the nose I know but who says we can't have fun right!

Today I had the realisation that gravity is a true constant. From what I can deduct all other forces can be turned on or off, e.g. heat, light, kinetic energy.... Why does energy have this force? And are there any other forces that are constantly outputting?

Hi StevieJoseph - That's great! Keep up the studies and follow your dreams.

I'm not sure I understand the question (so feel free to come back to me). What you mention are not forces like the force of gravity. Along with gravity, there are four fundamental forces - the other ones are electromagnetic, strong nuclear and weak nuclear. These operate over varying distances, and all weaken as you move away from them, but they don't turn off.
 
Nov 18, 2019
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Hi Dr. Joe,

It's wonderful that you are back to answer our questions. Here is my question:

The article for "GPS" on the wikipedia has a sentence: "The satellites carry very stable atomic clocks that are synchronized with one another and with ground clocks."

Does that mean these clocks are synchronized to show the same absolute time observed from all satellites reference frames and the ground reference frame, which contradicts special relativity's claim: time is relative and simultaneous events observed in one inertial reference frame must not be simultaneous observed from another inertial reference frame?
 
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Apr 5, 2021
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Got another one for you Dr. Joe:

Can an active star reach such a mass that it’s own light won’t be able to escape, as is the case with black holes? Black holes emit jets (I think) but would these type of stars emit anything and if not would they be suitable dark matter candidates?

Thanks
 
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DrJoePesce

Verified Expert
Mar 31, 2020
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414
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Hi Dr. Joe,

It's wonderful that you are back to answer our questions. Here is my question:

The article for "GPS" on the wikipedia has a sentence: "The satellites carry very stable atomic clocks that are synchronized with one another and with ground clocks."

Does that mean these clocks are synchronized to show the same absolute time observed from all satellites reference frames and the ground reference frame, which contradicts special relativity's claim: time is relative and simultaneous events observed in one inertial reference frame must not be simultaneous observed from another inertial reference frame?
Thanks Xinhang Shen – While I'm not a GPS expert, the clock on board the satellite is able to compare to a similar clock on the Earth because relativistic corrections are made. The satellite's clock is further from the mass of the Earth, and so its clock runs faster than a clock on Earth's surface. In order to be able to calculate its location, that difference is known and the GPS system corrects for it.
 

DrJoePesce

Verified Expert
Mar 31, 2020
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Got another one for you Dr. Joe:

Can an active star reach such a mass that it’s own light won’t be able to escape, as is the case with black holes? Black holes emit jets (I think) but would these type of stars emit anything and if not would they be suitable dark matter candidates?

Thanks
Hello suneritz, Thanks! For any star, no; only a black hole. Or more precisely, the singularity, because its gravitational field is so extreme, would create a situation where the escape velocity is the speed of light (and not allow light to escape).

The jets aren't emitted by the black hole (nothing is coming OUT of the black hole, if that's what you were thinking), but by reactions in the region near the black hole. The gravity of the black hole is providing the energy that drives the jet, but the jet isn't emanating from the black hole (just near it).

Give me a little more info about what you are thinking is an active star and I can maybe refine my answer!
 
Nov 18, 2019
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Thanks Xinhang Shen – While I'm not a GPS expert, the clock on board the satellite is able to compare to a similar clock on the Earth because relativistic corrections are made. The satellite's clock is further from the mass of the Earth, and so its clock runs faster than a clock on Earth's surface. In order to be able to calculate its location, that difference is known and the GPS system corrects for it.
Many thanks for your quick reply. But Special relativity tells us that simultaneous events observed in one inertial reference frame must not be simultaneous observed in another inertial reference frame, i.e., clocks synchronized relative to the ground frame must not be synchronized relative to the satellite frames no matter how you correct them, which has been denied by the fact that all the clocks on the GPS satellites and on the ground are synchronized relative to all satellite frames and the ground frame.
 
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