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The possible disappearance of a massive star in the galaxy PHL 293B

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Re: The possible disappearance of a massive star in the galaxy PHL 293B

#41

Post by kijin »

saiya-jin wrote: post #22
Jolter wrote: post #21

Earlier quoted context omitted.

That is my impression also. Stars/objects being swallowed by black holes tend to emit a large amount of radiation as it happens, over longer periods. Someone correct me if I'm wrong.

Maybe stupid question - what would happen to the star, if it actually 'collided' with black hole - ie black hole flew right through its core, not just casually going nearby, trapping each other and black hole slowly sucking it dry? I would expect the thing to be over rather swiftly, albeit probably with some accretion disc still generating some radiation.

A head-on collision with a black hole will likely produce a very noticeable explosion.

Black holes don't just vacuum up all the matter around them silently. Any matter falling into a black hole, not just the accretion disk, emits radiation. This radiation causes surrounding matter to expand outward, counteracting the gravity of the black hole. A black hole trying to eat an entire star at once will quickly exceed its Eddington limit [1] and most of the remaining matter will be blown away.

[1] https://en.wikipedia.org/wiki/Eddington_luminosity

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#42

Post by stargazer-3 »

mellosouls wrote: post #19
raxxorrax wrote: post #8

Sometimes astrologists make me smile: > important sources of ionizing photons Nothing better than a morning with cereal, milk and ionized photons. Wikipedia says that LVB often form clouds around them from their violent outbursts that are sometimes miss-classified as supernovae. We will probably have to wait if it pops up again.

Sometimes astrologists make me smile Nothing makes astronomers smile more than being called astrologists.

We smile on the outside yet cry on the inside.

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#43

Post by teruakohatu »

antognini wrote: post #2

To provide a little bit of context for this work, one of the open questions in astronomy is how core collapse supernovae work. Computational scientists have struggled for a long time to get simulations of core collapse to explode. Typically to get an explosion they have to artificially insert a "piston" somewhere in the system that kicks the system outwards during the collapse and triggers the shock wave. Over maybe…

Very interesting. Do you know the theoretical probability that at least one observable star will collapse/disappear during any given earth year?

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#44

Post by menybuvico »

JoeAltmaier wrote: post #37
Someone wrote: post #33

Earlier quoted context omitted.

Easier: if they build the frame for the sphere first, then added (gigantic) panels one at a time, a part filled with panels might have moved into our line of sight.

Or maybe they built them all in a higher orbit spaced apart, then simultaneously decelerated them all so they fell as one into a Dyson sphere! Have to have some kind of process, why not that one?

Self-propelled modular elements that are built separately, and then placed and connected to others.

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#45

Post by dredmorbius »

xorfish wrote: post #18
sheerun wrote: post #16

So they hypothesize it either collapsed to a black hole without supernova or stopped fusion. They don't mention it might just might have been swallowed by black hole.

Wouldn't that be a slow process?

Slow and exothermic.

A star would be unlikely to directly enter an event horizon but would instead orbit the black hole (with resulting doppler-shift accelerations detectable on Earth via spectral analysis), and strong emissions from IR to x-ray frequencies as matter was ripped from the star by tidal forces and drawn into the event horizon.

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#47

Post by rini17 »

saiya-jin wrote: post #22
Jolter wrote: post #21

Earlier quoted context omitted.

That is my impression also. Stars/objects being swallowed by black holes tend to emit a large amount of radiation as it happens, over longer periods. Someone correct me if I'm wrong.

Maybe stupid question - what would happen to the star, if it actually 'collided' with black hole - ie black hole flew right through its core, not just casually going nearby, trapping each other and black hole slowly sucking it dry? I would expect the thing to be over rather swiftly, albeit probably with some accretion disc still generating some radiation.

Before the actual head-on collision the star would be spaghettified(that's actual term, see below) by the black hole's gravity and that... is not a silent process, with exception of supermassive black holes.

https://en.wikipedia.org/wiki/Spaghettification

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#48

Post by lmilcin »

sandworm101 wrote: post #26
pja wrote: post #15

Earlier quoted context omitted.

It’s totally plausible. But if the core of your star is sufficiently massive then the initial collapse takes it over the Chandrasekhar limit & it forms a black hole immediately. Then the rest of the stellar material just falls into it. The fine details vary depending on mass, composition & spin of the rest of the material: if the star is spinning fast enough an accretion disk might form and drive jets which is one po…

>> Then the rest of the stellar material just falls into it. Spherical chickens in a vacuum. This would be true of a non-spinning black hole. In reality they all spin. The star was spinning before collapse. So a tiny amount quietly falls in, but the bulk of the outer shell quickly accelerates, energizes, jets form and generally the massive releases of energy blasts material away.

Having part of the star form accretion disc and then slowly radiate the energy is entirely different from the star converting significant part of its mass into energy and radiating it in couple of hours.

Also jets are highly directional and you have good chance to be away from the cone.

I am not a physicist but I suspect that extremely active star turning into black hole might be much less luminous than the star itself. Accretion disks can be very luminous but this is typically for very large holes in the centers of galaxies. Because we observe these huge stars only because they are so highly active, the act of converting it to much less luminous system might be undistinguishable from the star disappearing.

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#49

Post by eisstrom »

vagab0nd wrote: post #40
antognini wrote: post #2

To provide a little bit of context for this work, one of the open questions in astronomy is how core collapse supernovae work. Computational scientists have struggled for a long time to get simulations of core collapse to explode. Typically to get an explosion they have to artificially insert a "piston" somewhere in the system that kicks the system outwards during the collapse and triggers the shock wave. Over maybe…

Thanks for the great explanation. Are we tracking the spectra of everything visible in the sky? How much data is that?

In short: No, we cannot do that at the moment.

We have photometric all-sky surveys that can map the entire sky (visible from the telescope location) during a night up to a certain brightness. But those only take images of the sky, not spectra (Zwicky Transient Facility and the planned Vera C. Rubin Observatory).

What we also have are integral-field spectrographs which can take 2D images with a twist: there is one image for every ~0.1nm from 480nm to 950nm. You take one exposure with the instrument and you get a stack of thousands of images. If you go through the stack at a fixed spatial position you get the spectrum. The problem is that the integral-field spectrograph with the largest field-of-view is already huge (it is called MUSE at is located at the Very Large Telescope). And its field-of-view is "only" 1 arcmin^2 (1 deg = 60 arcmin), which is by far too small for large surveys. If you wanted to image the whole sky each night with MUSE clones, you would need several millions of them. A single MUSE exposure is about ~5 GB in the end but there are intermediate data products which are about 10 GB, if I remember correctly.

Re: The possible disappearance of a massive star in the galaxy PHL 293B

#50

Post by eisstrom »

7373737373 wrote: post #7
antognini wrote: post #2

To provide a little bit of context for this work, one of the open questions in astronomy is how core collapse supernovae work. Computational scientists have struggled for a long time to get simulations of core collapse to explode. Typically to get an explosion they have to artificially insert a "piston" somewhere in the system that kicks the system outwards during the collapse and triggers the shock wave. Over maybe…

Is there a project that shows which portions of the sky are currently viewed by which telescopes? Also, how can researchers request/rent usage of telescopes (especially satellite-based ones)?

I have experience only with the Very Large Telescope run by ESO in Chile, maybe what I write is only valid there.

There is usually no real schedule of targets for ground-based telescopes. There are two ways chosen at the telescope: either the astronomer who wrote the application is sitting there and decides what to do, or the staff goes through a list of approved programs and looks for objects that can be observed. This depends on the constraints described in the program (usually atmospheric conditions and height of object above horizon). Which target is chosen next is usually decided during the observation of the last target, there is no real schedule.

This is of course different for robotic telescopes (which is absolutely not the standard), like the Hubble Space Telescope but also ground-based robotic telescopes. But I'm not aware of a live feed of the pointing coordinates for them.

What one could do is regularly query the ESO archive[1] as finished observations appear there immediately (I think) and contain coordinates (just enter night: "2020 01 01" and maybe chose type: object).

In case of the Hubble Space Telescope and also ESO's telescopes, you write a proposal containing the science case, the requested time and instruments, and related previous experience, submit it before a deadline (twice each year for ESO) and hope for the best. The acceptance rate for the HST is currently ~20% [2]. It's a bit better for ESO telescopes. If you are successful you do not have to pay anything. ESO even pays your flight and hotel next to the telescopes in the middle of a desert [3].

The situation is totally different for American telescopes (as far as I know), where you either belong to an institution that has telescope time or not.

[1] http://archive.eso.org/eso/eso_archive_main.html [2] https://www.stsci.edu/contents/newsletters/2019-volume-36-is... [3] https://en.wikipedia.org/wiki/ESO_Hotel

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