Betelgeuse To Blow Up Soon — Or Not

rubycodez writes "A wave of 2012-related hoopla has hit the internet about the star that makes the 'right shoulder' of Orion the hunter: Betelgeuse. Astronomer Phil Plait once again puts rumors to rest. The star will indeed explode as a type II supernova, and when it does it will be brighter than Venus when viewed from Earth, though not as bright as the full moon. It will be visible in the night sky for weeks, and could be visible in the day sky for a short time. But that event could happen today or 100,000 years from now, or as much as a million years from now. Since Betelgeuse is over 600 light-years away, its violent death will not harm Earth in any way, but will definitely provide a huge bonanza of scientific information about supernovae. As geeks, we can only hope the core of Betelgeuse undergoes catastrophic failure in our lifetime."

Comments

Soon?

[RabbitWho]

What they're saying is it might have blown up around 600 years ago... or not

Re:Soon?

[Anonymous Coward]

Relativity says that the photon coming from Betelgeuse experiences no time when it travels those 600 light years. So the travel time is zero. If we see the star explode in 2020 then it would have exploded in 2020.

IANAP but light does have a travel time: the speed of light is finite. However, the photon does not experience travel time because it's travelling at the speed of light.

Re:Soon?

[Kjella]

Long story short, our full motion is measured relative to the background radiation. The earth rotates around itself, around the sun, the sun rotates around the milky way and the milky way is moving itself. In total we move about 0.2% of lightspeed, and time dilation is relative to the fraction of c squared so time goes about 0.0004% faster than at rest. Imagine you stuck your finger in still water, the circle it'd make would continue to grow and the wave would go on forever but get thinner and thinner. Same thing with the universe, the distance to the edge keeps increasing but the earth and moon isn't being pulled apart by space "stretching". All this is really on a much grander scale though, in terms of a planet 600 light years ago it's like asking if you can find your way down to the corner store without taking into account that earth is round.

The difficulty is in trying to get an accurate angle measurement, even taking pictures from both sides of the earth we only get a ~13000 km wide angle which is small when you're trying to see an object ~5000000000000000 km away. For Betelgeuse wikipedia lists the distance as 643 ± 146 ly so the uncertainty is almost 300 ly. If we could travel even a tiny bit in any direction that'd matter on a stellar scale and photograph the sky we'd have much, much, much better estimates on the distances. That said, we can still do a lot more from earth or near earth than we have so far and there's plans for far better telescopes than today, first up probably the James Webb Space Telescope in 2014 or 2015. Also ground based telescopes keep getting larger and better, even though the atmosphere limits them somewhat.

Re:Soon?

[guruevi]

I would suggest you to read Einstein's "Relativity: The Special and General Theory". He explains it pretty well. It's available for free from a number of sources as part of Project Gutenberg (free on iTunes Book Store, 0.99 for the Kindle, ...).

Re:Soon?

[Anonymous Coward]

I am a physicist (student), but I've never been awesome at astrophysics, so grain of salt with all of this. You raise a bunch of good questions. So first: How do we know how far away Betelgeuse is? Per Wikipedia, estimates of its distance have varied widely over the last hundred years, from ~100ly to ~1000ly, with the current one being ~640ly. We guess stars' distance with a combination of parallax (only good if they're close or really big--Betelgeuse is really big), apparent magnitude (how bright they seem from here), how hot they are, how big they are, what type they are, etc. These are all interrelated: Betelgeuse is a cool star, but puts out a ton of light, so therefore it must be really big, which means it must be ~this far away, etc.

As for how fast things are going, you can't talk about speed without a reference point. You have to pick a spot to consider as stationary to talk about how fast things are going relative to it. You can talk about the speed of Earth with respect to the sun, the speed of the sun with respect to the galactic center, and the speed of the galaxy with respect to other galaxies, but you can't really about about the speed of Earth through space in general.

Relativistic effects are present at any velocity, and this is in fact how the speeds of stars in the galaxy are measured relative to each other and to the galactic center. Most stars away from the center and the outer rim of the MWG orbit at about 210-240km/s, so even if you figure stars on opposite sides of the galaxy you have a typical relative star-to-star speed of less than 500 km/s. Time dilation effects for things moving away from one another go as t*sqrt(1-(v/c)^2), which gives you ~t*0.999999 for v=500km/s and c=speed of light. That means that during one second on Planet A, it looks like ~0.999999 seconds pass on Planet B. So--these things are really tiny, and don't matter too much. They're measurable though that we can measure stellar velocities with respect to galactic centers that way, though. Doppler effect equations are here.

That's inside of galaxies--stars don't move too fast. Galaxies, on the other hand, can be moving really quickly relative to one another. We might see other galaxies moving at 9/10 the speed of light, relative to us.

In all systems expect for galactic clusters, the forces binding particles together (gravity, electromagnetism, nuclear forces) are strong enough to keep inflation from affecting the distances between particles. So, clusters of galaxies are moving away from one another, but electrons aren't pulling away from protons. Also, while as far as we know the speed of light is constant, inflation is the cause of the redshift in the Cosmic Microwave Background radiation. This is radiation from just ~380,000 years after the Big Bang that has been stretched out from inflation so much that while it originated at ~3000 Kelvin, we see it as ~2.75K Wikipedia.

Re:Soon?

[Teancum]

How do we actually know that the wave/particle/whatever I see when I glance up at Betelguese is about 600 years old. It seems to me that we would need to know a few things first, before we could calculate that:

How we know the distance to Betelguese is due to Stellar Parallax and other stellar distance measurement systems that use the parallax as a baseline. This is a system of measurement that is roughly the same what is used for surveying land using a compass and a transit, but applied to astronomical object.

The point is not that the light is so old but that the star is so far away that based upon our understanding of physics that it would take about 600 years (give or take some.... the number isn't exact) for that light to reach the Earth. Quite literally, Betelguese is "600 light years" or the distance that light takes 600 years to travel at 300,000 km/second before it gets to the Earth. If you prefer to use kilometers, miles, or furlongs for measurement I can do the unit conversion but when dealing with those kind of distances it is much more convenient to stick with either parsecs or lightyears as a distance measurement.

BTW, Betelguese is actually a "close" star in a broad sense, considering that the nearest stars to the Earth besides the Sun are about 4-5 light years away. It is still far enough away that even stellar parallax is not really working well and needs other ways to measure the distance, but "roughly 600 light years" is a good approximation. The main Wikipedia article goes into more detail specific to this star.

As for the other factors you are putting into there, the main thing is to point out the Einstein described that the speed of light is constant in all directions from all points of view. In terms of getting into the esoteric philosophical minutiae, you can plow yourself into metaphysics if you want to that is to me more like contemplating the existence of your belly button and what implication it might have if it is missing from your abdomen. Compared to the speed of light and the uncertainty of the measurement of the distance to this star, worrying about minor tweaks that could distort the distance measurement in this fashion is irrational and not worth the effort of refuting or even acknowledging.

Re:Soon?

[Ruie]

Stellar parallax is usually measured using positions of the earth at different points of the orbit around the sun, which provides a much longer measurement base.

Re:Soon?

[ultranova]

Einstein's theories dictate that nothing can go as fast as c.

Actually, no: they are based on the observation that the speed of light relative to you doesn't change as you accelerate, which of course means that you can never catch it.

And of course your statement is incorrect anyway, as light is something and goes as fast as c. So do all massless particles, for that matter. So do chances in electromagnetic and gravitational fields.

Relativity says nothing about faster than c.

Relativity states that to go faster than c is to travel in time. In other words, things going faster than c will violate causality. That's pretty much up there with point out that something results in perpetual motion engines, as far as strength of refutations go.

Re:What about Ford Perfect?

[GreatDrok]

I don't know about Ford Perfect, but Ford Prefect may well have an issue with this.

Re:Already happened?

[dsanfte]

Calm down, he's obviously talking about his own inertial reference frame. And within his frame, he's correct.

Re:Already happened?

[Beryllium Sphere(tm)]

You can run a perfectly valid Newtonian clock-syncing algorithm when all parties are moving relative to each other at much less than the speed of light. That's the case here.

For any speed less than c, you preserve the order of events, and as soon as you say what the distance is, you're committed to talking about a fixed elapsed time because the speed of light is invariant.

The statements "Betelgeuse is 600 light years away" and "We're seeing it as it was 600 years ago" are equally valid. They're both approximately true for anyone who's moving slowly relative to us and Betelgeuse.

Someone in a relativistic starship who's racing the light from the supernova will report a shorter time, because she's just behind the light, and will truthfully report a shorter distance, equal to the (invariant) speed of light times the (her frame) measured time.

Re:Let's hope that..

[mrsquid0]

It is extremely unlikely that Betelgeuse will produce a gamma-ray burst. The current thinking is that supernovae only produce gamma-ray bursts in stars that have been stripped of their hydrogen envelopes. Betelgeuse still has most of its hydrogen, and there is not enough time to lose it before the supernova is likely to happen. Even if Betelgeuse does produce a gamma-ray burst the bursts occur along the rotation axis of the star, and Betelgeuse's rotation axis is not pointed towards us. Fortunately, we do not have to worry about a gamma-ray burst from Betelgeuse, because it is close enough that such a burst would be rather nasty for us.