APOD: NGC 6240: Merging Galaxies (2015 May 21)

[Chris Peterson]

If our galaxy collided with another, I assume that the matter (gas, dust, dark, etc) of both would be 'thrown about' in many and varied unpredictable ways. Although not very dense, would such matter 'thrown' in our direction be sufficient to collapse the heliosphere of our sun and magnetosphere of the earth, and expose us to the raw interstellar/intergalactic environment? And if so, (assuming we survived the other effects of the collision) would that not be fatal to us in any case?

All that dust and gas, even at its densest, still represents a harder vacuum than we can readily achieve in a laboratory. It would have no impact on stellar systems at all.

[Craine]

Black holes merging. Not something you see every day.

They happen pretty often. Every day, in fact. Estimates are from one to a hundred every million years for a Milky Way size galaxy. When Advanced LIGO comes on line, the nominal estimate for detections is 40 per year.

That's news to me. I thought they're very rare and very energetic and that no one has seen one yet.

Yeah, that number seems odd for black hole mergers. I thought stellar collisions in a galaxy our size were in the range of ~100 every million years. So, perhaps he meant that?

[Chris Peterson]

Black holes merging. Not something you see every day.

They happen pretty often. Every day, in fact. Estimates are from one to a hundred every million years for a Milky Way size galaxy. When Advanced LIGO comes on line, the nominal estimate for detections is 40 per year.

That's news to me. I thought they're very rare and very energetic and that no one has seen one yet.

You are correct that nobody has seen one yet. That doesn't mean they are rare.

That said, there may be some confusion here. Most black hole mergers occur when binary black hole systems merge. The merger of supermassive black holes is certainly far less common. LIGO's current sensitivity is only sufficient for detecting a 10 solar mass binary black hole collision every few decades. That number goes up to 40 for Advanced LIGO (with a high degree of uncertainty, given that we don't have good numbers for the number of binary black hole systems... but the detection range is from one or two a year to several hundred a year).

[geckzilla]

Oh, yes, I was thinking of supermassive black holes. I have heard of LIGO and the starting up of Advanced LIGO but don't know much about it.

[bystander]

...
I have heard of LIGO and the starting up of Advanced LIGO but don't know much about it.

http://asterisk.apod.com/viewtopic.php?t=34187

[Ron-Astro Pharmacist]

Add to that the LISA Pathfinder mission and science may soon get a "gravitational assist" to current knowledge.

http://www.esa.int/Our_Activities/Space ... r_overview

http://science.nasa.gov/missions/st-7/

http://en.wikipedia.org/wiki/LISA_Pathfinder

It sure seems this year is going to have plenty of action in space.

[Tctampa]

After 400 million years have the two Galaxies completed the merger?

In almost every reasonable interpretation, they are as we see them. Because time and space are tied together, and "now" is generally defined by the speed of light.

It would be better to ask what this particular collision will look like in 400 million years.

That's what I was asking.

[Boomer12k]

At first, I thought it was M82...then checked....400mly????? Ok...not M82....

Really nice good shot of it.

:---(===) *

[Craig Willford]

If our galaxy collided with another, I assume that the matter (gas, dust, dark, etc) of both would be 'thrown about' in many and varied unpredictable ways. Although not very dense, would such matter 'thrown' in our direction be sufficient to collapse the heliosphere of our sun and magnetosphere of the earth, and expose us to the raw interstellar/intergalactic environment? And if so, (assuming we survived the other effects of the collision) would that not be fatal to us in any case?

I would think we can draw some conclusions from the condition of our own Milky Way galaxy. I do not recall seeing a map of our galaxy showing tidal wings that I would expect from past collisions with M31, but there seem certainly to have tidal flares on the Large and Small Magellenic Clouds (LMC and SMC). The latter leads me to think that there have been one or more collisions of the Milky Way with the LMC and SMC before, likely since elementary life evolved on Earth. Perhaps such small collisions, occurring closer to the galactic core perhaps (where the center of gravity is), might not effect us too much out here on a spiral arm. The former makes me wonder: have there been no collisions of the Milky Way and M31 yet? That collision will give us an answer.

[Craine]

There are simulations of what will happen when our own Milky Way will collide with Andromeda. For instance:
https://www.youtube.com/watch?v=4Q0Hkea8bXU

For non-professionals I'd recommend the Universe Sandbox simulator. You can play around with all kinds of things, including galactic mergers.
http://store.steampowered.com/app/72200/
But a new version is about to come out later this year.

[Chris Peterson]

The former makes me wonder: have there been no collisions of the Milky Way and M31 yet? That collision will give us an answer.

These galaxies have never collided, nor passed near enough each other to create significant tidal distortions. That collision will perhaps give some species answers, but not ours.

[Ann]

The former makes me wonder: have there been no collisions of the Milky Way and M31 yet? That collision will give us an answer.

These galaxies have never collided, nor passed near enough each other to create significant tidal distortions. That collision will perhaps give some species answers, but not ours.

No, because it will happen so far into the future that our species isn't going to exist at that time. Bear in mind that Homo Sapiens has only existed for a few million years at most, and the collision between the Milky Way and Andromeda is not going to happen for several hundred million years. At best we can hope that some descendant of ours is going to be there and watch the events unfold.

But the collision of two supermassive black holes ought to have a huge impact on the host galaxy or galaxies. I recently saw a BBC documentary about mass extinctions on the Earth. We were told a lot about the asteroid impact that killed the dinosaurs, but we were also told that scientists have found no signs of any other huge asteroid impacts that have caused mass extinctions on the Earth. On those other occasions when more than half of all life forms on the Earth have suddenly become extinct, the causes have been something else. According to the BBC documentary, the collision of continents or the tearing apart of continents due to plate tectonics have led to upheavals on the Earth that have caused mass extinctions.

It seems to me that the collision of supermassive black holes should cause worse destruction than the collision of continents. At the very least, it should release far more energy.

Ann

[Chris Peterson]

It seems to me that the collision of supermassive black holes should cause worse destruction than the collision of continents. At the very least, it should release far more energy.

Maybe, maybe not. The EM emission of merging black holes is not well understood. Indeed, merging black holes may represent a standard candle, with the intensity of the EM emission independent of the mass of the bodies. Most of the EM may come from the accretion discs of one or both black holes, meaning they might be no brighter than any AGN. There's a good chance that most of the energy released will be in the form of gravitational radiation, which should have no effect at all on the rest of the galaxy. So the worst problem for life in colliding galaxies might well be nothing more than nearby star forming regions and gravitational perturbation, and nothing so dramatic as merging supermassive black holes.

I expect it's something we'll know a great deal more about within just a few years. But nothing that will ever be of more than academic interest to humans.

[Chardonay]

If Life existed in either galaxy prior to the collision, is it likely to exist now? . . .GOD ! ! ! What a Show ! !

Maybe, maybe not. It depends on a lot of factors, particularly what impact the collision had on the exact segment of the galaxy where the inhabited planet was located. Of course, the collision "unfolds" over millions of years, and the effects of the collision also "evolve". I guess it also depends on how hardy the life forms were, and what characteristics the planet had that made it habitable.

Ann

Ann, yours is one of the best Asterisk* observations yet. Because of the nature of still photography most of us most of the time are tempted to think cosmological events are happening very quickly .. whereas the real time frame is so stupendously long any result can be imagined (and the interactions so complex no computer model could be made of the ultimate result.) And we must remember the observation recorded more than once on Asterisk* that when galaxies pass through each other individual stars in those galaxies do not come anywhere near touching each other as the distances are so vast between individual stars in each galaxy (?) Even two of the so called Black Holes merging will be done in such slow real time that they will be transformed, not destroyed. The Big Rip now, that is another picture entirely.

[Chris Peterson]

Even two of the so called Black Holes merging will be done in such slow real time that they will be transformed, not destroyed.

Black holes simply merge. They certainly aren't destroyed, and "transformed" doesn't describe the result except in the most trivial sense. Binary black holes dance around each other for millions of years, without much effect (except possibly a periodic light signature from their accretions discs). The final collision and merger, however, is very fast- nearly instantaneous.

[apache32]

Thanks to Chris P. & Craine for merger information very interesting, waiting for LIGO!

[Chardonay]

Even two of the so called Black Holes merging will be done in such slow real time that they will be transformed, not destroyed.

Black holes simply merge. They certainly aren't destroyed, and "transformed" doesn't describe the result except in the most trivial sense. Binary black holes dance around each other for millions of years, without much effect (except possibly a periodic light signature from their accretions discs). The final collision and merger, however, is very fast- nearly instantaneous.

Chris what is trivial about: Full Definition of TRANSFORM

transitive verb
1
a : to change in composition or structure
b : to change the outward form or appearance of
c : to change in character or condition

And I definitely and totally disagree with your "The final collision and merger, however, is very fast - nearly instantaneous." You are still thinking in slow earth time.

[Chris Peterson]

Even two of the so called Black Holes merging will be done in such slow real time that they will be transformed, not destroyed.

Black holes simply merge. They certainly aren't destroyed, and "transformed" doesn't describe the result except in the most trivial sense. Binary black holes dance around each other for millions of years, without much effect (except possibly a periodic light signature from their accretions discs). The final collision and merger, however, is very fast- nearly instantaneous.

Chris what is trivial about: Full Definition of TRANSFORM

A black hole is defined by its mass, electric charge, and angular momentum. After a merger, the resultant black hole has a new mass, charge, and momentum which are determined by those properties in the progenitors. By "trivial" transformation I mean that there's a simple change, but no change in quality or form. The final black hole is just a black hole with the mass, charge, and momentum of the original pair.

And I definitely and totally disagree with your "The final collision and merger, however, is very fast - nearly instantaneous." You are still thinking in slow earth time.

I'm not sure what you mean. A merger is something that happens in a fraction of a second.

[starsurfer]

What does this galaxy look like using an earthbound telescope? Is it visible. This is spectacular!

One of the most detailed images taken with a ground based telescope is this one by Adam Block taken with a 0.8 meter telescope (compared to the 2.5 meter HST). He also discovered a supernova in this image.

[DavidLeodis]

I like to know at least the date(s) an image was acquired but knowing that the ESA rarely release that information (unlike the Hubble NewsCenter and Hubble Heritage websites) I still thought I would try to see if it was available through the image's Exif data I was able to obtain through the Hubble ESA website. To my surprise in the Exif data I found that the image create date was apparently "January 12, 2115". The January 12 may or may not be correct but, unless it is an image sent back from the future, I doubt that the 2115 year is correct!

[geckzilla]

This one is a simple matter of typing NGC 6240 into the search box at the Hubble Legacy Archive, David. http://hla.stsci.edu/hlaview.html

You can ignore all the datasets that didn't come from ACS or WFC3. So in this case the observations were done in February 2006 and August 2012.

[DavidLeodis]

Thanks geckzilla for your help, which is appreciated . I think I would have struggled to find the imformation otherwise.

I wonder why the Hubble European is so reluctant to reveal such basic information as the date(s) an image was acquired?

[geckzilla]

I wouldn't say that they're reluctant to share any information. It's more about not crowding the website with a lot of information that only a small percentage of users is interested in. NASA's HubbleSite has a tab format to accommodate the extra info and the trade off is that it is much more confusing to many users. ESA's is simple and generally more user-friendly for casual space image lovers. Two different design philosophies in action.

[addseo1115]

Thanks for sharing.