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View Full Version : That's Not a Comet, that's a Star



Fraser
2007-Aug-15, 07:11 PM
If you take a quick look at the photograph with this story you'd think you're looking at a comet. I've actually got it cut down the image a little to fit the website. ...

Read the full blog entry (http://www.universetoday.com/2007/08/15/thats-not-a-comet-thats-a-star/)

Terry Gush
2007-Aug-16, 02:18 AM
Mira (Latin for "Wonderful") is living up to it's name (source: http://en.wikipedia.org/wiki/Variable_star)

From the big picture of Mira A's tail....it looks more like an arc than a straight line. Is Mira gravitationally captured by some bigger system?

Variable stars are some of Dr Pamela Gay's favourite things...I wonder what her take on this developement is?

iantresman
2007-Aug-16, 09:53 AM
Original press release and hi-res images (http://www.galex.caltech.edu/MEDIA/2007-04/)

Mira is traveling at 130 km/s (80 miles/s), our Sun orbits around the Milky Way at 217 km/s (135 mi/s). I wonder if our Sun leaves a tail too? I would presume not as it's sheathed in the heliosphere, so I wonder what happened to Mira's heliosphere?

01101001
2007-Aug-16, 01:30 PM
I wonder if our Sun leaves a tail too? I would presume not as it's sheathed in the heliosphere, so I wonder what happened to Mira's heliosphere?

It might leave a slight something now, but things will pick up when the sun becomes a red giant like Mira.

antoniseb
2007-Aug-16, 01:38 PM
Original press release and hi-res images (http://www.galex.caltech.edu/MEDIA/2007-04/)

Mira is traveling at 130 km/s (80 miles/s), our Sun orbits around the Milky Way at 217 km/s (135 mi/s).

This is a misconception on your part. Mira is traveling at 80 miles/s relative to the interstellar medium in our neighborhood. The Sun is going somewhere closer to 3 miles/s through the this medium.

01101001
2007-Aug-16, 02:05 PM
This is a misconception on your part. Mira is traveling at 80 miles/s relative to the interstellar medium in our neighborhood. The Sun is going somewhere closer to 3 miles/s through the this medium.

Oh, that won't be impressive at all. Poor Sol.

iantresman
2007-Aug-16, 04:28 PM
This is a misconception on your part. Mira is traveling at 80 miles/s relative to the interstellar medium in our neighborhood. The Sun is going somewhere closer to 3 miles/s through the this medium.

Which makes sense if galaxies rotate as a whole (ie flat rotation curves (http://en.wikipedia.org/wiki/Galaxy_rotation_curve)).

I wonder then, what the relative motion of the galaxy is, with respect to the intergalactic medium... and if all galaxies (or stars within) leave a trail?

antoniseb
2007-Aug-16, 04:56 PM
I wonder then, what the relative motion of the galaxy is, with respect to the intergalactic medium... and if all galaxies (or stars within) leave a trail?
I'm not sure what you mean. Mira is probably a member of a galaxy currently in the later stages of merging with the Milky Way, hence its large relative velocity.

The local interstellar medium seems to be moving about the same speed as the average of the stars around us. The intergalactic medium is not that well-known to us as far as direction and speed of flow. What we do know is the aggregate of the shapes of the absorption lines we see in the spectra of stars in nearby galaxies. This is difficult to measure, since the total number of photons from such objects is so small.

neilzero
2007-Aug-16, 08:40 PM
For the sun to circle the galaxy at 217 km/s, but moving 3 km/s with respect to the steller medium; the steller medium (locally) must be orbiting the galaxy in about the same orbit as our sun? Neil

antoniseb
2007-Aug-16, 10:46 PM
the steller medium (locally) must be orbiting the galaxy in about the same orbit as our sun? Neil
Yes, otherwise the ISM particles would be falling in toward the center.

Jerry
2007-Aug-22, 03:04 PM
This is a misconception on your part. Mira is traveling at 80 miles/s relative to the interstellar medium in our neighborhood. The Sun is going somewhere closer to 3 miles/s through the this medium.
One has to wonder if the motion of Mira relative to the ISM has been accelerated by an asymetric shedding of Mira's atmosphere. I don't know of a rule that says once a star decays and becomes an unstable thermal engine, the atmosphere of the star must remain spherically centered. Like supernova remnants, Mira may be self-propelled. Perhaps we should look at the rings found in supernova remnants (rings which predate explosions), and see if the distribution of matter within this rings is consistent with a 'tailing' prior to the collapse to a dwarf-type star.

publiusr
2007-Aug-24, 06:36 PM
I'd like to see some computer gen images of this