Can someone explain how the trailing matter has enough energy to glow for over 30000 years? Without the star nearby to replenish it, I can't figure out how that much energy is stored for that long. I can understand that much energy being released as the star moves through the interstellar gas, but where is the energy coming from 30k years later?

Actually, I just did some rough calculations, and at roughly 64 km/s, that would mean it's been glowing for more like 60k years? Is its velocity that variable?

^Ya know dude, I'm not really sure about all of that. I might have known, but I got kicked out of MIT's astrophysics program for immoral experiments with gravity. I don't think those kittens suffered. Too much.

Astronomers are not totally sure about the ultraviolet fluoresence of the Mira trail. They think the bow shock of this star (the star is travelling at almost 300,000 miles per hour relative to the matter the star is colliding with) is producing enough heat to cause the gas to fluoresce. Think HUGE amounts of REALLY hot matter spread out in a gigantic tail in an environment with little conductive or convective heat loss. This thing would glow for a long time. (Like nebula surrounding the remains of a supernova where only the released energy of the event long ago has the shells of gas still glowing.)

re: velocity - The 64km/s (≈ 143000mph) is radial velocity, so I guess it's not relevant, but I can't find any reference to its linear(?) velocity, i.e., velocity relative to the material it's shedding.

I'm pretty confident it's not releasing energy on the scale of a supernova. Material from a supernova is ejected at much higher velocities (orders of magnitude greater). And doesn't the remaining neutron star or black hole continue to provide energy to the surrounding shell?

This star is flying balls to the wall relative to the matter its colliding with. The energy of said collision is enormous. I think thats where a lot of its coming from.

I'm not questioning that a tremendous amount of energy would be released as the star blasts through interstellar material. The question is how can that matter continue to emit energy so long after the source of energy is long gone. Note that the brightness of the tail is fairly similar for a very long time/distance. The star passes by, shedding some of its matter and the collision emits a lot of energy. A kind of wake is left behind, but instead of continuing to expand (and interact with more matter), it just emits radiation near where the star passed, and at a similar level for tens of thousands of years.

In the case of a supernova remnant, there is an expanding shell of (a vastly greater amount of) matter that continues to slam into the surrounding material. When a supernova first blows up it can outshine the galaxy it's in. The expanding shell of material continues to sweep up more matter and the whole system grows much dimmer very quickly. Also, a supernova remnant (usually?/always?) has a continuing source of energy from whatever is left over at the center.

As I wrote to KP, I'm definitely not an astrophysicist - just trying to wrap my head around this really weird phenomenon.

Tags for this video have been changed from 'mira, shooting, star, ultraviolet, tail, spitzer, galaxy, evolotion, explorer' to 'mira, shooting, star, ultraviolet, tail, spitzer, galaxy, evolution, explorer' - edited by Issykitty

Ok. Johnny. I will try to answer your questions and if I can't I know someone who can.

angular velocity=velocity/radius

Also, my guess is: You are trying to backwards calculate the energy. You have to use the reletavistic correction for something going this fast.

I have to pick up some business cards and go to the gym. I will reply more in a couple hours.

>> ^jonny:
re: velocity - The 64km/s (≈ 143000mph) is radial velocity, so I guess it's not relevant, but I can't find any reference to its linear(?) velocity...

http://www.nasa.gov/mission_pages/galex/galex-20070815.html
http://en.wikipedia.org/wiki/Mira

The simple answer is that it is a star.

Stars, like ours, emit radiation as a result of nuclear fusion. As it moves through space, the radiation creates a bow, where that radiation interacts with hydrogen. My guess is the hydrogen is excited to a higher energy state. When it decays, it emits the ultraviolet light that is whipped around the star in the shape of a tail.

You can't treat Mira with the same math and logic as a comet, because it produces its own energy.

>> ^MycroftHomlz:
You can't treat Mira with the same math and logic as a comet, because it produces its own energy.

I wasn't thinking of it like a comet, which does not emit energy (does it?). A comet's tail is created from material being stripped away by solar wind, and is visible because of reflected sunlight, correct?

The question about velocity was not a lack of understanding of basic physics, but a lack of a good description of Mira's linear velocity relative to the material through which it's passing. The wiki article only vaguely mentions it in passing, and notes its radial, not angular, velocity in the sidebar. Thanks for the nasa link, though, as that answers it exactly. It's linear velocity is roughly 130 km/sec, which translates to a distance of roughly 13 light years in 30000 years. Cool - that was the easy part.

But apparently I'm not getting my main question across very clearly. I understand that stars use fusion to generate the energy they are emitting. But the distal end of that tail is 13 light years away from the star and has been emitting UV radiation for over 30000 years. My question is not about the amount of energy released, but the rate at which it is being released. Are you suggesting that excited hydrogen atoms are taking over 30000 years to return to a low energy state without undergoing any other interaction after the star has passed?

A vast amount of energy is transferred to the interstellar hydrogen gas in a fairly short amount of time as Mira zooms by, but then the hydrogen is taking 30000 years to release that energy? That's what I'm not understanding. I mean, if hydrogen atoms can store that much energy for that long, then I'd recommend one of you smart physicist types start looking into hydrogen based batteries!

It could be a little more complicated than that...but essentially yes.

In all reality the neighboring interactions could kick the electrons back to excited states and they could decay again. You follow. So even thought it might not take that long typically for it to decay, the fact is it's neighbor has emitted exactly the right energy to excite it back up into the excited state. My guess is you can't ignore nearest neighbor interactions and think of it as a linear process.

Secondly, hydrogen was just a guess. It could be something else that takes long to decay, a hydrogen isotope. Lots of material emit radiation in the UV for astronomically long times.

I don't know anything about physics, but here's a stab in the dark. What about the stars own gravity. What if the matter is being dragged along by the stars gravity, only at a slower rate than the star is traveling? We are so far away it just appears that the matter is not moving. When in fact the star is draggin it keeping the discarded matter really hot.

Also from the pic it looks like it is traveling through something, disrupting some field or gas we cannot see. Kind of like a rock passing through water or thick smoke. If you look closely at the pic you can see some distinct rippling affects and even a spiral affect close to the tail of the star. Something is distrupting the flow of that matter. Another gravity field produced nearby perhaps? Maybe not.

So the rate of decay would be slow as the star drags along the matter keeping it hot and whatever it is passing through providing the constant fuel to maintain the burn. Over time the matter slowly decelerates, cools and fades from our vision.

All in all it is still a guess.

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