APOD: The Case of the Missing Star (2017 Jun 06)

[APOD Robot]

The Case of the Missing Star

Explanation: What's happened to giant star N6946-BH1? It was there just a few years ago -- Hubble imaged it. Now there's only a faint glow. What's curiouser, no bright supernova occurred -- although the star did brighten significantly for a few months. The leading theory is that, at about 25 times the mass of our Sun, N6946-BH1's great gravity held much of the star together during its final tumultuous death throes, after which most of the star sank into a black hole of its own making. If so, then some of what remained outside of the black hole likely then formed an accretion disk that emits comparatively faint infrared light as it swirls around, before falling in. If this mode of star death is confirmed with other stars, it gives direct evidence that a very massive star can end its life with a whimper rather than a bang.

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[mindheart]

How the heck did anyone ever discover that???

[alter-ego]

How the heck did anyone ever discover that???

About 8 years of monitoring 1 million supergiants for failed supernovae using the Large Binocular Telescope, and follow up images of this rare event from Spitzer and Hubble.
http://www.skyandtelescope.com/astronom ... iscovered/
https://arxiv.org/abs/1609.01283
http://iopscience.iop.org/article/10.1086/590053/pdf

[reedkantor@comcast.net]

Your grammar needs more careful attention. "Brightened?"

[CharlesE]

The two photos certainly show the increase in resolution between the early years of Hubble and the current equipment.

[starsurfer]

Ooh an intergalactic mystery!
Maybe it was the casualty of interstellar warfare?

[bystander]

http://asterisk.apod.com/viewtopic.php?t=37219

[BDanielMayfield]

Nice discovery. I say this because, whenever something new comes out in astronomy, I like to view the observation, finding or theory in terms of what it might mean for the prospects of life in the universe.

In the beginning, the Big Bang produced only the lightest elements; H, He, Li and a trace of Be. All other elements needed for life like C, O, N, Fe and every other naturally occurring element was and are being fused inside stars and in the enormously energetic explosions of supernovae. Without these SN blasts, the elements required for life would never make it out into space where they can later condense into planets like Earth.

So SN have had a vital role to play in making the universe habitable. They have done their work so well that now, the mid planes of spiral galaxies like ours are darkened by interstellar dust made of all the elements needed to produce rocky planets like ours. But, viewed from the life positive viewpoint, enough already with the SN please. Life prospects in starburst galaxies currently undergoing frequent SN detonations would have to be tougher due to higher odds of your planet being sterilized by a nearby SN. And indeed, the SN rate has happily for us fallen off greatly over the billions of years since our galaxy formed.

Therefore, if the number of SN is reduced by a process that causes some to be snuffed out by direct collapse into massive Black Holes, it is a good thing for life in general in the universe, imo.

Bruce

[Chris Peterson]

So SN have had a vital role to play in making the universe habitable. They have done their work so well that now, the mid planes of spiral galaxies like ours are darkened by interstellar dust made of all the elements needed to produce rocky planets like ours. But, viewed from the life positive viewpoint, enough already with the SN please. Life prospects in starburst galaxies currently undergoing frequent SN detonations would have to be tougher due to higher odds of your planet being sterilized by a nearby SN. And indeed, the SN rate has happily for us fallen off greatly over the billions of years since our galaxy formed.

I think that the risk from supernovas is greatly overstated. They would have to be very close indeed to sterilize a planet. And what is "life"? If we take Earth has an example (it is, after all, the only example we have), "life" means single-celled pond scum (all there was until recently). That's not going to get killed off by even a very close supernova. Indeed, the radiation of a supernova might be just what's needed to increase the rate of evolution. A supernova really only presents significant risk to complex, land-based life. And even if that were wiped out, it's likely it would be back again within a few hundred million years. Assuming complex life requires billions of years to form, it will only occur in systems with stable planetary orbits, which means in less dense regions of galaxies where supernovas will be at safe distances.

So overall, I think it's reasonable to view supernovas as an overwhelmingly positive thing when it comes to life.

[BDanielMayfield]

So SN have had a vital role to play in making the universe habitable. They have done their work so well that now, the mid planes of spiral galaxies like ours are darkened by interstellar dust made of all the elements needed to produce rocky planets like ours. But, viewed from the life positive viewpoint, enough already with the SN please. Life prospects in starburst galaxies currently undergoing frequent SN detonations would have to be tougher due to higher odds of your planet being sterilized by a nearby SN. And indeed, the SN rate has happily for us fallen off greatly over the billions of years since our galaxy formed.

I think that the risk from supernovas is greatly overstated. They would have to be very close indeed to sterilize a planet. And what is "life"? If we take Earth has an example (it is, after all, the only example we have), "life" means single-celled pond scum (all there was until recently). That's not going to get killed off by even a very close supernova. Indeed, the radiation of a supernova might be just what's needed to increase the rate of evolution. A supernova really only presents significant risk to complex, land-based life. And even if that were wiped out, it's likely it would be back again within a few hundred million years. Assuming complex life requires billions of years to form, it will only occur in systems with stable planetary orbits, which means in less dense regions of galaxies where supernovas will be at safe distances.

So overall, I think it's reasonable to view supernovas as an overwhelmingly positive thing when it comes to life.

You make good points Chris, but (likely rare) life on our level would be more vulnerable than single celled life. Even if the risk is low, less risk is better, I would think. I do like and agree with your conclusion that SN are "an overwhelmingly positive thing when it comes to life."

The more we learn, the more we may come to appreciate black holes and the roles they play as well.

Bruce

[BDanielMayfield]

Another point occurred to me: Suppose that SN blast intensity just rose with progenitor mass, and no stars collapsed directly into black holes. Wouldn't the rate of the even more dangerous hypernovae be greater? The laws of physics benefit life by limiting both the power and the frequency of these detonations.

Bruce

[Chris Peterson]

Another point occurred to me: Suppose that SN blast intensity just rose with progenitor mass, and no stars collapsed directly into black holes. Wouldn't the rate of the even more dangerous hypernovae be greater? The laws of physics benefit life by limiting both the power and the frequency of these detonations.

You're venturing into the fine-tuning argument, or the anthropic principle. Life is highly dependent on all the laws of physics being just what they are. But that's not to say that a universe with different rules wouldn't produce an analog to what we call "life" in our universe.

[BDanielMayfield]

You're venturing into the fine-tuning argument, or the anthropic principle.

True.

Life is highly dependent on all the laws of physics being just what they are.

Also true.

But that's not to say that a universe with different rules wouldn't produce an analog to what we call "life" in our universe.

Possibly, but it is an unproven assumption. On the other hand it can be shown that changes to the laws of physics result in universes where life is clearly impossible, such as ones where no stars form, etc. Which is easier, finding another set of laws that would work for life, or fouling things up for life?

Bruce

[RJN]

Your grammar needs more careful attention. "Brightened?"

Thanks. This and another two typos (around and including "sank") have been fixed. Also "some of" added before "what remains", as not all of the mass likely ended up in the accretion disk.

- RJN

[Chris Peterson]

But that's not to say that a universe with different rules wouldn't produce an analog to what we call "life" in our universe.

Possibly, but it is an unproven assumption. On the other hand it can be shown that changes to the laws of physics result in universes where life is clearly impossible, such as ones where no stars form, etc. Which is easier, finding another set of laws that would work for life, or fouling things up for life?

It isn't possible to "find another set of laws". My own thinking is that any universe that allows for complexity would produce life. That there's nothing in the least special about the laws of our universe.

[vendetta]

I agree with Chris on the overestimated role of supernovae in sterilizing planets. There are way too many unknowns regarding how far away a SN must be, how much radiation will reach the ground depending on the thickness and composition of a planet's atmosphere, etc.

Something else that is not always pointed out is that high energy radiation is very easily absorbed by 2-3 meters of water, so marine life wouldn't be dramatically affected. Here on Earth, marine life conquered dry land in just a few hundred million years(*), so in order for SN to have a measurable impact on (land) life across the Milky Way, exoplanetary systems would have to be subject to nearby SN explosions more frequently than that. The spatial and temporal distribution of SN is nowhere high enough to keep a decent amount of exoplanets constantly sterilized.

That being said, just in case I wouldn't like to be too close to one

JC

(*) I don't think this can be easily extrapolated to life in other planets, but at least it provides a handy order-of-magnitude estimate.

[heehaw]

Aren't there surveys going on now looking repeatedly at star fields for transiting planets? Surely they should include algorithms for detecting vanishing stars. Maybe the rate of stars turning into black holes is too small? one a year in our whole galaxy? or what? I don't know!

[douglas]

Red supergiants are known for their bloated sizes and big dusty stellar winds. Their supernova pathways are also well mapped, yes?

Did this star follow a red supergiant's SN pathway?

" .. N6946-BH1, experienced an outburst in 2009 March, first brightening to >10^6 L [solar] but then fading to 10^5 L[solar] below its pre-outburst luminosity."

" .. observations over the 10 years prior to the optical outburst reveal a very luminous (10^5:3 L[solar]) star
that remained at a constant brightness between 1999 and 2005, but then faded in the optical between 2005 and 2008 as it brightened at 3.6 micorometers."

This is not the behavior of a star going supernova: "The source appeared quiescent in LBT observations on 5 July 2008, ... and by .. 20 Oct 2009 the source had already dropped below the progenitor flux in all optical bands."

"The main evidence disfavoring N6946-BH1 being a SN `impostor' is that after eruptive mass loss a star is expected to be overluminous, not subluminous .. "

Chandra has not been used on this object yet.

Future surveys will note such behaviors from red supergiants?

https://arxiv.org/pdf/1609.01283.pdf

[Nitpicker]

Aren't there surveys going on now looking repeatedly at star fields for transiting planets? Surely they should include algorithms for detecting vanishing stars. Maybe the rate of stars turning into black holes is too small? one a year in our whole galaxy? or what? I don't know!

It must also be easier to detect a dim star becoming much brighter, than a dim star becoming much dimmer. Star N6946-BH1 is/was in the supernova factory that is the Fireworks Galaxy (NGC 6946). There are doubtless many people keeping an eye on this galaxy. But the star only had an apparent magnitude of about 18 before it went missing, so its vanishing was probably only detectable by the better instruments.

I thought the average rate of supernovae was roughly one per galaxy per century. I have no idea what the comparable rate would be for the alternative black-hole fate of stars.

And I could be wrong, but I don't think the surveys for exoplanets are looking at nearly as many stars as the surveys for supernovae. The exoplanet surveys are all within the Milky Way (I think).

[LLAP]

Hi
Anyone notice a change in colour for one of the stars bottom left of the photos? One photo has it blue the other yellow/orange - quite different. All the other stars in both photos seem to match up ok colour wise.

[Nitpicker]

The two photos certainly show the increase in resolution between the early years of Hubble and the current equipment.

Yes, the installation of the WFC3 instrument in 2009, increased the pixel resolution by about 2.5 times, compared with its predecessor, WFPC2, which had an operating life of about 15 years on the HST.

[ta152h0]

and here it comes, at the speed of darkness

[neufer]

and here it comes, at the speed of darkness

MACBETH: All our yesterdays have lighted fools

• The way to dusty death. Out, out, brief candle!
  Life's but a walking shadow, a poor player
  That struts and frets his hour upon the stage
  And then is heard no more: it is a tale
  Told by an idiot, full of sound and fury,
  Signifying nothing.

dork (n.) "stupid person," 1967, originally U.S. student slang

darkness (n.) Old English deorcnysse, from dark + -ness. Figurative use is recorded from mid-14c. The 10c. Anglo-Saxon treatise on astronomy uses þeostrum for "darkness."

[CWGraces]

Does it matter that there appear to be a few new, (or newly bright,) stars in the field?

Go up in the field around 11 O'clock. There is a triangle group of blue stars. In the second picture there are two new orange stars that are not noticeable in the first.

Diana