MadSci Network: Astronomy

Re: Do truly large stars ever eject actual mini - stars?

Date: Mon Jan 31 12:46:11 2000
Posted By: Jeff Brown, Faculty, Astronomy
Area of science: Astronomy
ID: 947746849.As

Flares can be spectacular, but the amount of matter involved is small, compared to the mass of the Sun. The Sun loses mass now at a rate of about one ten-billionth (ten to the minus 10 power) of a solar mass per year. This includes the solar wind and many flares in that year's time. Measured sustained mass loss rates for stars range up to about one ten-thousandth (ten to the minus 4 power) solar mass per year; stars that have these prodigious mass loss rates are very massive stars near the end of their lives. Even at those elevated mass-loss rates, though, more than a year's worth of matter would have to be stored up to reach a star's worth. That "storing up" doesn't happen. Instead, the matter is lost as gas or dispersed dust particles blown out in a wind or in flare-like eruptions, and is far too diffuse to recollapse under its own gravity (which it would have to do to make a new star) without spending a long time cooling off.

Episodic mass loss can exceed these rates for short periods of time. The most spectacular mass-loss events to have been observed -- other than those of supernova explosions! -- are probably those of eta Carina (called eta Argus at the time) back in the early 1840's. (We didn't know what was going on back then, of course.) This southern-hemisphere star has varied in brightness drastically over history; at the time of that outburst, it was the second brightest star in the sky. Most of the time it is at or below the threshhold of the naked eye.

Hubble Space Telescope has taken images of the eta Carina nebula showing the material ejected in this eruption, including images from different dates so that you can see the motion of the ejecta. While fascinating things are going on there, the matter is too hot and too diffuse to be making new stars now.

There is also the point that even if a single object (like a star) were ejected, unless there was third body near the system to take away some of the energy and momentum of the ejected object, that object would wither be thrown completely out of the old system or it would just fall right back into its point of origin. Our spacecraft reach orbit by having rockets burn with variable rates all the way up from the launch point to orbit. Something kicked out all at once, like a cannon shot, might be in an orbit, but without a third body there to alter that orbit its orbit will pass through the launch point again -- that is, the ejected object will fall back down to where it came from.

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