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Fraser
2004-Oct-04, 05:14 PM
SUMMARY: Living at the centre of the Milky Way would be beautiful, but dangerous, according to research from the Harvard Smithsonian Center for Astrophysics. Every 20 million years or so, a ring of gas and dust 500 light-years away from the middle of the galaxy collapses, beginning a furious period of star formation, which then sets off a series of supernovae. A planet in the area would be completely sterilized of life as star after star explodes. The next starburst period in the Milky Way is likely to happen in about 10 million years, but don't worry, we're far enough away that nothing would happen to the Earth.

What do you think about this story? Post your comments below.

lswinford
2004-Oct-04, 08:08 PM
I had asked about this in a previous discussion elsewhere and now it is answered for me, thanks. One thing I wonder, besides if 500 lightyears is a safe distance, involves the geometry of these events. A fairly frequent depiction of a pinwheel-type galaxy such as ours includes a fair halo above and below, with occassional star clusters and a bit of haze. I wouldn't want to be guilty of "two-dimensional thinking" as the expression goes. I wonder if we don't also have some ejection of stellar material from these blasts that eventually rain down upon the galaxy arms from their gravitational attraction countering the spent forward momentum of the stellar ejecta (the haze). This then would infuse some fresh samplings of elements light and heavy. I wonder how we would detect such and if this is the case, would we need to be watching for waves of matter raining down, in correlation to previous waves of dispersal? This would sort of be waiting for the next echo or perhaps the kind of rain that is sometimes associated with battlefields wherein saturated air that is shook with a boom then dumps part of its water load. The next explosive event sends out a shockwave or flash that jostles the particles above and below the galaxy, giving fresh momentum for more to rain down upon the disk. Just a thought as I tried to picture this.

antoniseb
2004-Oct-04, 08:14 PM
Originally posted by lswinford@Oct 4 2004, 08:08 PM
I wonder if we don't also have some ejection of stellar material from these blasts that eventually rain down upon the galaxy arms from their gravitational attraction countering the spent forward momentum of the stellar ejecta (the haze).
Hi lswinford,

The stars in the halo are mostly very old stars that must be too lightweight to be creating any new supernovas. The heavier stars are already neutron stars and black holes. Your vision may be correct however for very early galaxies going through their original starburst activities.

GOURDHEAD
2004-Oct-08, 02:54 PM
Quoted from the article:

But the material can take its time getting there, and one way to postpone the inevitable is to form stars. In fact, during one of the massive ring collapses, there is more incoming gas than the black hole can handle.

"It would be like trying to fill a dog dish with a fire hose." Stark said. Therefore, most of the ring’s material goes instead into the starburst.

I would expect the physics of dog bowl filling to be somewhat different from that of adding material to a black hole. Another brain (mind) tearing assertion. Perhaps the conservation of angular momentum drives the material to velocities that propel its relativistic mass to values that tend to choke the process. Star forming in such a dynamic environment must be a challenge.

geokstr
2004-Dec-04, 01:16 AM
I have two questions:

1) Is that 20 million years, plus or minus a few millions? It would seem a bit presumptuous to assume they've got that time frame nailed down.

2) What if the effects of this starburst are NOT so benign and innocuous as they think it is?

I read just recently that the earth has experienced mass extinctions every 26 million years or so. Speculation now is some sort of periodic meteor or comet shower. However, is it just a coincidence that these time periods are relatively similar?

What if the starbursts cause an outpouring of radiation or material of some kind and/or at some level which is lethal to life even from that distance? It's worth pondering.

antoniseb
2004-Dec-04, 02:47 AM
Originally posted by geokstr@Dec 4 2004, 01:16 AM
1) Is that 20 million years, plus or minus a few millions?
Yes, the frequency is not precisely known, and is probably not precisely regular either. We might know the figure within 20% or so.

2) What if the effects of this starburst are NOT so benign and innocuous as they think it is?
For starters, the 26 million year theory is a myth. Take a look at this short paper about mass extinctions in history. Mass Extinctions (http://people.hofstra.edu/faculty/J_B_Bennington/137notes/extinction.html)
There were six mass extinctions in the last 600 million years, and they were not evenly spaced. The twenty-six million year thing was claimed by the people who were claiming that the Sun had a red-dwarf companion in a 26 million year highly elliptical orbit. This object was referred to as Nemesis. Since then other reasons were attributed by hacks and amateurs to this non-existent pattern of mass extinction, such as the Sun's up and down path throught the galaxy, and anything else periodic close to 26 million years.

This twenty-million year pattern of star burst activity is nothing to worry about.