Milky Way to collide with Andromeda Galaxy

[Xenus]

Galaxies have collided before it is not the be all end all. they were not destroyed som merged the others ended up different from when they started but were not anilated.

 

[Bobbler]

Hmmm, better not confuse "astrologists" with "astronomers" - I suspect both groups would be rather offended by being associated with the other one.

Err, yea... not sure what I was thinking, hah.

 

[nutball]

It literally destroys whole galaxies;

No it doesn't!

astronomers call these Death Stars.

No we don't!

A simulation has been created of what would happen to Earth if the closest star to this galaxy went hypernova, and although it wouldn't destory the planet, rest assured nothing would survive.

That "simulation" is regarded with a great deal of scepticism by anyone with a serious scientific background (it's little more than a bunch of assumptions coddled together with numbers plucked from the air). The media love it of course, because it's gigadeath!

 

[arjan de lumens]

While GRBs can release large amounts of energy, the vast majority of the energy is apparently beamed out from its poles, and if you are not within that beam, the GRB looks rather unremarkable. This means that early estimates of the actual power in a GRB are now considered vast overestimates.

Incidentally, if you're afraid of GRBs, check out a star named "Eta Carinae". It is a notoriously volatile blue giant star ~7000 light years away from us. This star is the heaviest star known to man at ~150 solar masses and is expected to go hypernova/GRB on us very soon now (well, "very soon" on an astronomical timescale, which could still mean thousands of years).

 

[London Geezer]

While GRBs can release large amounts of energy, the vast majority of the energy is apparently beamed out from its poles, and if you are not within that beam, the GRB looks rather unremarkable. This means that early estimates of the actual power in a GRB are now considered vast overestimates.

Incidentally, if you're afraid of GRBs, check out a star named "Eta Carinae". It is a notoriously volatile blue giant star ~7000 light years away from us. This star is the heaviest star known to man at ~150 solar masses and is expected to go hypernova/GRB on us very soon now (well, "very soon" on an astronomical timescale, which could still mean thousands of years).

You mean it's already happened but we won't see it for a long time?
Sometimes space time delays/shifts/messes leave me speechless... You know, for that half a second or so...

 

[K.I.L.E.R]

Arjan, wouldn't the resulting GRB destory our atmosphere?

 

[arjan de lumens]

Arjan, wouldn't the resulting GRB destory our atmosphere?

AFAIK, current estimates of GRB power indicate that if Eta Carinae goes GRB straight on Earth, it is still too far away to do serious damage to our atmosphere (if it was closer, like, say 1000 light years, then it would be quite deadly, but 7000 light years is believed to be rather safe), so to us people on the ground it will probably just be a spectacular light show.

Satellites, astronauts and other small stuff outside the atmosphere would probably be fried quite badly, though.

 

[K.I.L.E.R]

Wouldn't the people looking at the light show go blind or would our atmosphere protect us from it?

 

[arjan de lumens]

Wouldn't the people looking at the light show go blind or would our atmosphere protect us from it?

That I actually don't know. Looking directly into an ongoing GRB might pose dangers similar to looking directly into a solar eclipse (usually small permanent blind spots rather than general blindness), but the actual GRB itself only lasts for a few seconds, after which it should be fairly safe to look at it.

 

[nutball]

The optical afterglow of a GRB can last for minutes. There was a famous burst in 1999 (with the telephone number 990123) which reached 9th magnitude, which is getting close to be a naked eye object (you'd certainly have seen it with a pair of binoculars).

http://nis-www.lanl.gov/~rotse/grb990123/

This was at a redshift z=1.6 (~7Gpc)! If one of these went off in our galaxy you'd certainly see it!

 

[arjan de lumens]

OK, then we can do some (rather speculative) math. If we assume that Eta Carinae will reach the same strength as 990123, then: 990123 is placed about 10^6 times times farther away than Eta Carinae, so the light intensity of an Eta Carinae GRB will be about 10^12 times stronger (light intensity falls off by about square of distance). 1 "magnitude" in astronomy corresponds to a factor of 2.512, so Eta Carinae would be ~30 magnitudes stronger than 990123, as seen from Earth, placing its apparent magnitude around -21 - not quite as strong as the mid-day Sun (-26), but much stronger than the full Moon (-12). Given that Eta Carinae due to distance would take up a much smaller section of the sky than the Sun, I suspect that if you are unlucky enough to look directly at it at the peak of such a burst, you would get a small permanent burn scar on your retina.

 

[ANova]

No it doesn't!

No we don't!

That "simulation" is regarded with a great deal of scepticism by anyone with a serious scientific background (it's little more than a bunch of assumptions coddled together with numbers plucked from the air). The media love it of course, because it's gigadeath!

Ninety somewhat percent of our understanding of the universe and our existence comes from assumptions. Some believe it, even though you may not. True, none of it may be correct, but we won't know until it happens, assuming it ever does.

 

[nutball]

Ninety somewhat percent of our understanding of the universe and our existence comes from assumptions. Some believe it, even though you may not. True, none of it may be correct, but we won't know until it happens, assuming it ever does.

The calculation of the gamma-ray fluence at Earth from a GRB in our galaxy is a relatively trivial calculation to make. It's the conclusions drawn about the effects that this energy input would have on the atmosphere, and from there the effect on life on Earth that are highly speculative.

That the conclusions of the work hit the newspaper headlines at precisely the same time that the author had just launched his new book is coincidence, you reckon?

 

[Neeyik]

OK, then we can do some (rather speculative) math. If we assume that Eta Carinae will reach the same strength as 990123, then: 990123 is placed about 10^6 times times farther away than Eta Carinae, so the light intensity of an Eta Carinae GRB will be about 10^12 times stronger (light intensity falls off by about square of distance). 1 "magnitude" in astronomy corresponds to a factor of 2.512, so Eta Carinae would be ~30 magnitudes stronger than 990123, as seen from Earth, placing its apparent magnitude around -21 - not quite as strong as the mid-day Sun (-26), but much stronger than the full Moon (-12). Given that Eta Carinae due to distance would take up a much smaller section of the sky than the Sun, I suspect that if you are unlucky enough to look directly at it at the peak of such a burst, you would get a small permanent burn scar on your retina.

Hmm, I only get an apparent magnitude of -7.7; my workings could be totally wrong of course but I first calculated 990123's absolute magnitude by using M = m-5(log10D-1) where m is the apparent magnitude, D is the distance in parsecs and M is the absolute magnitude. So if 990123 had an apparent mag of +9 at a distance of 7Gpc, then M = 9-5((log10 x 7 x 10^6)-1) = -20.2 I know that one has to use luminosity distance for objects further away than, say, 10~50kpc but I'm assuming that nutball's figure for 990123 is the lum dist! Anyway, if -20.2 is right and eta carinae is the same, then one can find the apparent magnitude in reverse; m = M+5(log10D-1) = -20.2+5((log10 x 3.2 x 10^3))-1) = -7.7

 

[arjan de lumens]

Ninety somewhat percent of our understanding of the universe and our existence comes from assumptions. Some believe it, even though you may not. True, none of it may be correct, but we won't know until it happens, assuming it ever does.

Coming first with a bunch of doomsaying, then hiding behind the "we cannot know" shield, strikes me as useless fearmongering.

 

[arjan de lumens]

Hmm, I only get an apparent magnitude of -7.7; my workings could be totally wrong of course but I first calculated 990123's absolute magnitude by using M = m-5(log10D-1) where m is the apparent magnitude, D is the distance in parsecs and M is the absolute magnitude. So if 990123 had an apparent mag of +9 at a distance of 7Gpc, then M = 9-5((log10 x 7 x 10^6)-1) = -20.2 I know that one has to use luminosity distance for objects further away than, say, 10~50kpc but I'm assuming that nutball's figure for 990123 is the lum dist! Anyway, if -20.2 is right and eta carinae is the same, then one can find the apparent magnitude in reverse; m = M+5(log10D-1) = -20.2+5((log10 x 3.2 x 10^3))-1) = -7.7

Ligt intensity falls off as 1/distance^2, not 1/distance.

 

[Neeyik]

Ligt intensity falls off as 1/distance^2, not 1/distance.

I know but I don't think your calcs are right with the figures though - distance to 990123 is 7 x 10^6 pc whereas EC is about 3.2 x 10^3 pc. So with I being proportional to 1/d^2 then that puts the ratio of intensities of Iec/I99 = (1/Dec^2)/(1/D99^2) = D99^2/Dec^2 = (7x10^6)^2/(3x10^3)^2 = 4.8x10^6 which seems quite different to 10^12. I don't think that I've made a mistake here but my astrophysics, even basic stuff, is pretty rusty!

Edit:

I ~ 1/d2

Ie/I99 = (7x10^6)^2/(3x10^3)^2 = 4.8 x 10^6

m99 - m = 2.5 log10 (Ie / I99)

9 - m = 2.5 log10 (4.8 x 10^6)

m = 9 - 2.5 log10 (4.8 x 10^6)

m = -7.7

 

[arjan de lumens]

I know but I don't think your calcs are right with the figures though - distance to 990123 is 7 x 10^6 pc whereas EC is about 3.2 x 10^3 pc. So with I being proportional to 1/d^2 then that puts the ratio of intensities of Iec/I99 = (1/Dec^2)/(1/D99^2) = D99^2/Dec^2 = (7x10^6)^2/(3x10^3)^2 = 4.8x10^6 which seems quite different to 10^12. I don't think that I've made a mistake here but my astrophysics, even basic stuff, is pretty rusty!

Umm, no. The numbers that nutball stated and I have been able to find on the distance to GRB 990123 are on the order of 10^9 parsecs, not 10^6.

 

[ANova]

Coming first with a bunch of doomsaying, then hiding behind the "we cannot know" shield, strikes me as useless fearmongering.

I merely asserted one possibility which I think has some relevency, however I can't pretend to know as fact and neither can you or nutball.

 

[Neeyik]

Umm, no. The numbers that nutball stated and I have been able to find on the distance to GRB 990123 are on the order of 10^9 parsecs, not 10^6.

Doh! I'd even read the darn distance right as being 7Gpc but in my head, used it as 7Mpc - lo and behold, you get -22.7 for m when use it right!