Two things are amazing (to me) about this picture.
1) When you look up in the sky at the Andromeda Galaxy, your retina is absorbing photons that have been screaming through space for 2.5 million years. If you were on the Earth then, you'd be hanging out with Smilodon, the saber-toothed cat. For 2.5 million years, those photons were freely zooming through space and time, and when you see them, those photons are gone forever, their energy powering a chemical reaction in the rods and cones lining your retina that enables you to see them. Those ancient photons were seen by nobody else but you, and they literally become a part of you.
2) In about 3.75 billion years, the Andromeda Galaxy, currently zipping through space toward the Milky Way Galaxy at 110 km/s (nearly 70 miles per second, or about 250,000 MPH), will collide with and merge with our galactic home. It's unlikely anything would happen to the majority of planetary systems in either galaxy (there's a lot of empty space in there) -- but the night sky (not from Earth, we'd probably be cooked by the Sun by then) sure would be beautiful. And bright.
Scientists even proposed the name for the new galaxy: Milkomeda.
Fun NDG quote regarding #1. It's 2.5 million years from our frame of reference, but an instant for the photon.
> Photons have no ticking time at all, which means, as far as they are concerned, they are absorbed the instant they are emitted, even if the distance traveled is across the universe itself.
Sometimes I sit outside with one of the sky/star apps and look for stars that are about the same light years away as I am old. It's neat to think about the light leaving that star when I was born and taking my entire life to reach me. The scale of the universe and our place in it is hard to fully comprehend.
> For 2.5 million years, those photons were freely zooming through space [...]
Imagine the faces of Penzias and Wilson when they learned that the noise in their horn antenna wasn't bird poop but photons traveling 14 billion years without interacting.
> the night sky (not from Earth, we'd probably be cooked by the Sun by then) sure would be beautiful. And bright
Brighter, yes, but not very bright. The density of stars will not increase very much. Currently, to see the Milky Way, you have to be out in the boondocks, far from cities and other light polluters - the thing is just so faint.
After the merger, perhaps it will get brighter, but the increase will not be spectacular. The brightness of the combined galaxy as seen from Earth will be dictated by the stellar density, which will not change much.
Especially on #2. The sheer size of the galaxy is so mind-boggling. So many stars, and each one could potentially have some form of life on a planet around it. And it's just one galaxy of billions (or is it trillions? I forget, but it's already so huge that it hardly matters). So far away that we can hardly conceive of the idea of ever going there. But wait, it's already coming to us! More quickly than any realistic form of propulsion we could come up with.
I was thinking a similiar thing last night when I read this news. What we observed through the Hubble telescope now about the Andromeda Galaxy happened 2.5 millions years ago. What is it actually doing right now? Is it still alive?
Yes. Our own galactic 'year' is 250 million years (the time it takes to rotate in place once). So 2.5 million years is about a galactic day (or maybe a weekend).
Question about #1: Where did the photons originate though? Did the Andromeda Galaxy create its own, or were these bounced off and we see (basically) the reflection?
The photons almost all originated in stars in the Andromeda Galaxy. A very small number reflected off of gas in the interstellar medium, but nothing your eye could detect.
>your retina is absorbing photons that have been screaming through space for 2.5 million years
according to QM idea of superposition collapse that photon has just decided to collapse in your retina while it had non-zero probability of collapsing into retina of an alien anywhere on that 2.5 million radius circle. That blows my imagination :)
1) When you look up in the sky at the Andromeda Galaxy, your retina is absorbing photons that have been screaming through space for 2.5 million years. If you were on the Earth then, you'd be hanging out with Smilodon, the saber-toothed cat. For 2.5 million years, those photons were freely zooming through space and time, and when you see them, those photons are gone forever, their energy powering a chemical reaction in the rods and cones lining your retina that enables you to see them. Those ancient photons were seen by nobody else but you, and they literally become a part of you.
2) In about 3.75 billion years, the Andromeda Galaxy, currently zipping through space toward the Milky Way Galaxy at 110 km/s (nearly 70 miles per second, or about 250,000 MPH), will collide with and merge with our galactic home. It's unlikely anything would happen to the majority of planetary systems in either galaxy (there's a lot of empty space in there) -- but the night sky (not from Earth, we'd probably be cooked by the Sun by then) sure would be beautiful. And bright.
Scientists even proposed the name for the new galaxy: Milkomeda.