Betelgeuse?

[theville24]

If betelgeuse was to explode, would it come towards earth?

[antoniseb]

If betelgeuse was to explode, would it come towards earth?

Are you asking if there would be a concentrated beam of energy coming toward Earth, or if any of the debris would come toward Earth?

[StupendousMan]

Yes, some of the material would come toward Earth.

Yes, it would look very bright -- just a dot, though, a very bright dot.

No, it wouldn't harm life on Earth.

[Shaula]

And by explode do you mean go supernova? There are directional supernova but what tends to happen is that energy and some matter is ejected - but the direction is random. The star itself would pretty much cease to exist so no, Betelgeuse would not come towards us. There is a chance some energy and mass might but it is a tiny chance. Tiny^2 in fact.

[jfribrg]

Rememer that Betelgeuse is one of the more distant stars that are visibile to the naked eye. It is easily visible because it is about as big as a star can be. If the Sun were only 10% as far away, we would still need a telescope to see it. If it did explode, I assume that there would be an expanding sphere of debris, some of which would head in our direction. Maybe millions of years from now some truly miniscule amount might encounter the solar system, but I suspect that most of it would have collided with nebulae and stellar winds from intervening stars. Whether any of that miniscule amount makes it through our own Solar wind to encounter Earth is very doubtful.

[chornedsnorkack]

The star itself would pretty much cease to exist so no, Betelgeuse would not come towards us.

Do you allege that Betelgeuse should explode as Type I supernova? Or as a pair instability supernova?

Other stars pretty much continue to exist, either as neutron stars or black holes.

And neutron stars which happen to be visible as pulsars are notorious for often having high peculiar velocities. A large proportion of them are not bound to Milky Way. Puppis A is notoriously as fast as 1500 km/s. And the faster pulsars are underrepresented among the known set, because fast pulsars far away outside Milky Way are difficult to detect at that distance.

Black holes are harder to detect than pulsars. What are the peculiar velocities of young black holes like?

From the rotation, magnetic fields and other observable traits of stars yet to explode as supernovae, is it possible to predict the peculiar velocity and direction of pulsar rays after explosion?

Should Betelgeuse set off towards us at 1500 km/s, like Puppis A, it would cover the 200 parsec distance in just 130 000 years. And while the diffuse supernova nebula will be rapidly slowed down by sweeping a bubble through interstellar gas, a pulsar is not so slowed down and pierces stellar fields and clusters at ease.

[CaptainToonces]

There are directional supernova but what tends to happen is that energy and some matter is ejected - but the direction is random.

The ejecta doesn't come out of the poles?

[CaptainToonces]

would it be possible to forecast a supernova by measuring the intensity of iron in the spectra, or whatever element directly leads to iron in the process?

[Shaula]

Do you allege that Betelgeuse should explode as Type I supernova? Or as a pair instability supernova?

Nope, just saying that Betelgeuse the large red thing will not be around. You may be reading too much into a throwaway comment there! Betelgeuse is not going to be a type I - wrong sort of star entirely.

would it be possible to forecast a supernova by measuring the intensity of iron in the spectra, or whatever element directly leads to iron in the process?

Not really - the outer layers stay dominated by H and He.

The ejecta may well be linked to the poles according to current theory - I should have read up on them first.

[astromark]

point. The moment we see that Betelgeuse has Nova'd its here.
It will have taken 640 light years for that light image to have reached here.
The energy stream you might be worried about is of NO concern to us.
It travels much slower and will have dissipated well before reaching Earth.
It is not expected any dangerous levels of radiation will reach here from Betelgeuse.

[Henry Krinkle]

point. The moment we see that Betelgeuse has Nova'd its here.
It will have taken 640 light years for that light image to have reached here.
.

Will we know it has gone supernova prior to the light reaching us? And by what means?

[Nick Theodorakis]

Will we know it has gone supernova prior to the light reaching us? And by what means?

I believe the neutrino pulse from a supernova briefly precedes the visible manifestation of such. So if the various neutrino detectors around the world started going wonky we'd know something was about to blow.

Nick

[Jens]

If betelgeuse was to explode, would it come towards earth?

I think others have already answered pretty well, but just for clarification, what do you mean by "it"?

[theville24]

thanks for the help!

[Tim Thompson]

This is a copy of a message I posted on another board in January ...

Betelgeuse is not 1300 light years (LY) away. It's more like 640 LY away. It is a massive single star (maybe 20 solar masses) and will eventually explode in a core collapse supernova. They are a dimmer class of supernova than a type Ia and can be expected to peak out at about absolute magnitude -18.5 (that's apparent magnitude -18.5 at the standard distance of 10 parsecs or 32.6 LY). At its much farther actual distance a Betelgeuse supernova should present itself to us with an apparent magnitude of about -12. The apparent magnitude of the full moon is about -12.5. That means the brightest you can expect a Betelgeuse supernova to look to us would be to rival the full moon for brightness. Since it would be a point source, and not half a degree across like the moon, it would certainly be visible in the daytime sky (Venus is visible to the naked eye in the daytime sky, if you look carefully, and its apparent magnitude is about -5 at its brightest). At night you could read by its light, if it indeed matches the full moon in brightness.

So we won't be picking up another sun, but we might pick up another full moon for a while. And to put us in real danger a core collapse supernova would have to be within 10 parsecs of Earth (Will a Nearby Supernova Endanger Life on Earth?). Betelgeuse is about 200 parsecs away and so too distant to do anything but look cute.

[eburacum45]

The idea of the Betelgeuse Remnant bulleting towards us at 1500 km/s is an intriguing one, but it would be an incredily lucky shot if it managed to get close enough to us to do any damage. (or an unlucky shot, depending on one's point of view).

[astromark]

Will we know it has gone supernova prior to the light reaching us? And by what means?

Please do reread post #10 you quoted me in part and asked this question... Yes there could be some indication of brightening or a sudden shrinking or dimming prior to its nova event. We might spot changes in the weeks leading up to..
REMEMBERING that it must have happened 639 and eleven months ago for us to see it tonight.

[CaptainToonces]

That means the brightest you can expect a Betelgeuse supernova to look to us would be to rival the full moon for brightness. Since it would be a point source, and not half a degree across like the moon, it would certainly be visible in the daytime sky

what's a "point source"? tell me how many microseconds of arc or whatever the actual size of it is. Now if you're talking about an object the same brightness as the full moon but stuffed into a size of say one arcsecond, then that would be 1800 times the light intensity per area. Wouldn't that be dangerous to look at?

[astromark]

It would seem you have answered your own question. A point source is a single point of very bright light.
Akin to looking at a arc welders rod. Its a long way away from being any risk to your eyesight. Unmagnified.
For us astronomers, we might need to use filters to protect our eyesight from the magnified single point light.

[Tim Thompson]

what's a "point source"?

A "point source" is anything that is smaller than the Airy Disk of your optical system. That means either it is s true geometric point or it is so small in angular size that your optical system cannot tell the difference between what you are looking at and a true geometric point.

tell me how many microseconds of arc or whatever the actual size of it is.

The measured angular diameter of Betelgeuse is about 0.05 arcseconds, but varies with wavelength over the range roughly 0.04 - 0.07 arcseconds, being somewhat larger in red & infrared than in visible light. This size also varies with time, since Betelgeuse is a pulsating red supergiant star. The ISI team from UC Berkeley reported in 2009 that Betelgeuse had shrunk by 15% in the period 1993-2008, so its angular size will vary considerably. However, the Airy Disk of the human eye is in the range 1-2 arcminutes. That's about 1200 times the angular size of Betelgeuse in visible light, so Betelgeuse will at all times present itself to the human eye as a point source, and that is what I originally meant.

Now if you're talking about an object the same brightness as the full moon but stuffed into a size of say one arcsecond, then that would be 1800 times the light intensity per area. Wouldn't that be dangerous to look at?

No, it would be 1800² or 3,240,000 times the light intensity per area (30 arcmin x 60 arcsec/arcmin = 1800; you are only looking at the linear relationship, but the area = pi*r²). But thanks to the Airy Disk in the human eye, supernova Betelgeuse will never appear to be anything but a "point source" and that has the angular size of the Airy Disk. So it will look to the eye as about 1 arcminute across, or about 900 times the light intensity per area. I don't see why that should appear to be anything other than a bright light. Certainly we encounter lights that bright in our man made environment on a regular basis.

[CaptainToonces]

Thanks Tim, your post is a lot more informative than Mark's.

I appreciate that you've provided the actual arclength of Betelgeuse since i was pretty sure it wasn't a singularity with an arclength of 0

It sounds like the Betelgeuse supernova just doesn't have intensity to threaten the human eye's biological health, even though it is such a massive amount of light energy crammed into a small area?

[astromark]

Then you should read that again... From planet Earth Betelgeuse does not, will not, have arc seconds of image...

0.05 arc seconds is a single point source. We have all said this... However just like the now famous 'Crab nebular'

The remnant of Betelgeuse will be growing to be a impressive nebular.

Of some visible size as yet unknown... but larger than a single point of light.

As to the brightness of the 'Nova' event of Betelgeuse. Do we really know what intensity it could reach ?

Looking into the eye piece while this event unfolds could harm your vision.

Telescopes have a unfortunate side effect... magnification of very bright points of light can be harmful if you stare.

Humanity is generally in NO danger.

[CaptainToonces]

0.05 arc seconds is a single point source. We have all said this...

No, it's not. It's 0.05 arc seconds of arclength. Using terms like "point source" is for specific mathematical purpose but does not describe reality. Just because your telescope doesn't resolve farther than 0.05 arcseconds does not make Betelgeuse a "point" in the sky, where the definition of a point is "In geometry, topology and related branches of mathematics a spatial point is a primitive notion upon which other concepts may be defined. In geometry, points have neither volume, area, length, nor any other higher dimensional analogue." (http://en.wikipedia.org/wiki/Point_%28geometry%29) Betelgeuse does in fact have arclength is therefore not a point.

[astromark]

I will not go down this road.. You seem to have missed the point.

Now using dot. as point.

It seems to be pointless to argue about so little...

Science has shown the image of this star... Its boiling heaving mass ready to let go of its mass...

But for the observer without the 10.4 metre scope... its a dot. That might brighten dramatically... We wait.

[Shaula]

No but it is a point source for the human eye which was the original issue. You are reading that as 'point' 'source' whereas it is 'point source' - Wikipedia. A point source is a source which is smaller than the resolution of the system used to image it. It is not a point.

[CaptainToonces]

I respect your opinions greatly Shaula, but if that is the meaning of "point source" then of what real use is term? It is misleading at best. If your telescope's maximum resolution is .1 arcsecond, then a dot that shows up there would be much better desribed as having a radius of .1 arcsecond instead of "0" that the word point implies. I was trying to calculate the light intensity per square inch (or in this case, square arcseconds). for the Betelgeuse supernova. Plugging 0 into that equation results in nonsense.

I was proposing the question of whether or not such concentration of light energy across a small square area could be biologically harmful to the eye. I don't know enough about ocular biology to say.

[Shaula]

Because knowing that for your eye the source can be modelled as a point makes the maths much easier. All you have to do is look at the diffraction limits for the eye rather than untangling the effects of non-zero size and the MTF of the receiving system. You can assume all the energy from the star falling over an area the size of the pupil is focussed to the sharpest image the eye can make.

Sorry if you don't find it useful but that is what point-source means. A key issue is that if you see a point that is as small a your telescope can resolve then that tells you nothing more than an upper limit on its size. Saying from that that the source is of such-and-such a size is as misleading as the term point-source! Astromark comes at this from an optics type background AIUI so would use the term as I described - I was just trying to explain why you were both right but wrong from each other's point of view. Unless I am reading too much into it you were talking about the size of the star irrespective of the system and pointing out that it was not a point, whereas Astromark was saying that for small instruments (like the eye) it is a point-source.

[CaptainToonces]

Saying from that that the source is of such-and-such a size is as misleading as the term point-source!

Not really. Take again the example of calculating the light intensity per square arcsecond. Plugging 0 in as the arclength of the object yields a light intensity of infinity. Whereas plugging in the minimum resolution of your measuring device yields a quite reasonable answer.

[Shaula]

It you are specifically talking about the size of the image then that is not misleading, if you are talking about the size of the object then it is. I guess it is a matter of semantics and background. I am used to saying that if an image of an object is the size of my system resolution then the object is point-source.

Your use of zero there is wrong, as you know because you got an infinity. The size of the object can be zero but the size of an image cannot be. Your calculations are being done in image space - you are performing two steps at once in a way. The two steps are:

Q: How big is my object?
A: Point source
Q: What is my system resolution?
A: X
Therefore the size of my image is X.

You skipped the middle bit and went straight into thinking about the object in image space.

[antoniseb]

Not really. Take again the example of calculating the light intensity per square arcsecond. Plugging 0 in as the arclength of the object yields a light intensity of infinity. Whereas plugging in the minimum resolution of your measuring device yields a quite reasonable answer.

Two things worth noting:
- There is about an arcsecond of atmospheric smearing for most observers.
- A lot of the light from the supernova comes from an expanding cloud of Ni56, which for something as near as Betelgeuse will be larger than an arc-second pretty quickly.