Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Yahya on 20/07/2018 15:32:31
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https://www.space.com/35290-star-explosion-expected-earth-sky-2022.html
what do you think of this ? what its image is supposed to be? big ? small ? lasting long?
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What kind of elements will be created in that meeting? I mean, the temperature should increase in it, shouldn't it?
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We're talking about a pair of stars some 1800 ly distant, which presently are too dim to see by the naked eye (~ magnitude 12)
The explosion should make it naked eye visible to the point that it will rival some of the brighter stars. In other words, people will be able to see a new star (nova) in the constellation of Cygnus for a short while
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Looking at the previously best-studied example of a "red nova" (V1309 Scorpii), it increased in brightness by 10 (astronomical) magnitudes, or by about a factor of 10,000 at the time of merger. The brightness then declined over a period of a month or so.
Similar behavior would take KIC 9832227 from magnitude 12 to magnitude 2, which would be very visible to the naked eye (provided it didn't happen while Earth was on the other side of the Sun).
The decreasing distance is due to tidal effects transferring angular momentum from the smaller star to the atmosphere of the larger star (gravitational waves have significant effects only on compact objects like neutron stars and black holes).
See: https://en.wikipedia.org/wiki/V1309_Scorpii
See the light curve at: http://inspirehep.net/record/1242804/plots
(Second graph on the page; the horizontal axis tick marks represent 10 days each.)
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Similar behavior would take KIC 9832227 from magnitude 12 to magnitude 2, which would be very visible to the naked eye (provided it didn't happen while Earth was on the other side of the Sun).
From where I live, close to 45 degrees N, the binary pair is always above the horizon. Thus it should be visible for some time at night during any month of the year.
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If KIC 9832227 follows the pattern of V1309 Scorpii, we can expect the merger to occur in several phases:
Before Merger:
- Outgassing: There is a very small amount of gas being flung out of the binary pair system, not enough to produce a visible disk.
- Spectrum: The spectrum shows two sets of spectral lines (one from each star) - when one star is moving towards us, the other is moving away, and then the roles reverse.
- Brightness: Over the orbital period (currently under 12 hours), there are two light peaks, when both stars are visible to us. But at some points in the orbit, the smaller star obscures part of the larger star, and at other points the larger star obscures most of the small star, producing two brightness dips.
Leadup To Merger
- Outgassing: Increasing amounts of gas are flung out of the binary star system, forming a visible disk. The disk envelopes the smaller star. The disk cools rapidly, so is "redder" than the parent stars.
- Spectrum: The smaller star is embedded in the disk, so it no longer shows as a separate set of spectral lines. But the larger star protrudes from the disk, providing spectral lines which are distinct from the spectral lines of the disk.
- Brightness: Light emission from the growing, glowing disk causes brightness to increase more than exponentially. Because the smaller star is buried in the disk, there is no longer the double-humped light curve.
During Merger
- Outgassing: Huge amounts of hot gas spray into space
- Spectrum: The hot gas dominates the spectrum
- Brightness: Brightness reaches a significant peak
During Merger
- Outgassing: Outgassing slows and stops.
- Spectrum: The hot gas dominates the spectrum
- Brightness: The gas disk cools over a period of months, with brightness decaying exponentially. Eventually, the new, disturbed star becomes visible.
What kind of elements will be created in that meeting?
Unlike the Sun, the larger star will be able to produce elements heavier than helium.
When the two stars merge, it will be even more massive and able to produce even heavier elements (up towards iron) as the star burns all its fuel.
I expect that it won't produce any particularly novel elements - just the sort of elements you expect from a more massive star.
The main question is whether the larger star is disturbed enough to go into a supernova in the short term, instead of waiting for it to exhaust all its fuel.
See: https://en.wikipedia.org/wiki/KIC_9832227
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Cool story; thanks for highlighting it!