Category: local group

These Are The Last Galaxies That Will Remain In Our Night Sky

“But beyond our backyard, all the other galaxies, groups, and clusters are accelerating away from us.

Once you go about 4-5 million light years away, dark energy causes space to expand faster than gravity attracts other objects across space.

Over time, every other galaxy will see its distance and recession speed increase from our perspective.”

Our Universe isn’t only expanding, but is accelerating. This means that every galaxy, group, or cluster that isn’t already gravitationally bound to us is receding from us at a faster and faster rate as time goes on. With 2 trillion galaxies in the observable Universe, only approximately 70 of them are bound to our Local Group. Everything farther than about 4 or 5 million light years away from us is unbound, and therefore will recede from us forever and ever, with their recession speeds and cosmic distances increasing over time.

Here are the last galaxies we’ll ever be able to see or visit, as the relentless expansion of the Universe causes their disappearance from our cosmic horizon.

Our Local Group Is Being Eaten, And We Just Found The Galactic Leftovers

“Two of the Milky Way’s larger satellites — the Magellanic Clouds — are interacting, forming stars, and on track to be devoured. But one of Andromeda’s satellites is even more interesting. M32 is the smallest galaxy in the Messier catalog: just 6,500 light years across, with ~3 billion solar masses of material. Its dense core houses a multi-million solar mass black hole, extremely unusual for a small galaxy. It suggests that M32 was once much larger, and has been partially cannibalized.”

Here in the local group, we have Andromeda, the Milky Way, and about 60 galaxies that are much smaller. Four of the top 10 galaxies are actually satellites of either the Milky Way or Andromeda. The Large and Small Magellanic Clouds are less than 200,000 light years from the Milky Way, with M32 and M110 in tight orbit around Andromeda. But M32 is no ordinary satellite! In a brand new study published today in Nature Astronomy, scientists took several pieces of evidence and combined them, concluding that M32 is actually a remnant of the third largest galaxy in the Local Group: M32p, which was mostly devoured 2 billion years ago by Andromeda.

In the Universe, all we have left are the survivors, but thanks to some fascinating galactic archaeology, we can reconstruct exactly where it all came from!

How Does Earth Move Through Space? Now We Know, On Every Scale

“Ask a scientist for our cosmic address, and you’ll get quite a mouthful. Here we are, on planet Earth, which spins on its axis and revolves around the Sun, which orbits in an ellipse around the center of the Milky Way, which is being pulled towards Andromeda within our local group, which is being pushed around inside our cosmic supercluster, Laniakea, by galactic groups, clusters, and cosmic voids, which itself lies in the KBC void amidst the large-scale structure of the Universe. After decades of research, science has finally put together the complete picture, and can quantify exactly how fast we’re moving through space, on every scale.”

It’s hard to believe, but despite being at rest here on the surface of Earth, we’re actually hurtling through the Universe in a variety of impressive ways. The Earth spins on its axis, giving someone at the equator a speed of some 1700 km/hr. Yet at even faster speeds, the Earth orbits the Sun, the Sun moves through the Milky Way, and there’s a great cosmic motion that applied to the Milky Way galaxy beyond even that. For a long time, we’ve been able to measure the total effect of all these motions, summed up, by measuring our motion relative to the cosmic microwave background: the leftover glow from the Big Bang. But it’s only very, very recently that we’ve identified the source of all the gravitational causes of this motion. While we’ve known of stars, galaxies, and the large-scale structure of where matter is, it’s new that we’ve quantified the effects of these great cosmic voids.

By combining everything together, we can finally explain the grand total of all of our cosmic motion through the Universe. Come get the full, complete story at last!

What Will The Death Of The Milky Way Look Like?

“On Earth, we’ve got another billion years or two before the oceans boil and the planet becomes uninhabitable. The Sun will heat up, swell into a red giant, fuse helium in its core, then blow off its outer layers and contract into a white dwarf. But new stars will pop up, too, and shine, and keep the galaxy alive and rife with stars far into the future. But even our own Milky Way will cease to exist: first as we know it, and later on, entirely. When enough time passes, there will be no stars, stellar remnants, or even black holes left at all. This is the cosmic story of the ultimate end of our home in space.”

In the far future, all the galaxies within our Local Group will merge together, with enough gas and stellar material to form trillions upon trillions of new stars. But the amount of fuel is finite, and gravitational interactions are chaotic. At some point, the star forming material contained in our galaxy will come to an end, while more and more stars and stellar remnants are ejected from the galaxy. What will be left, at that point? Just a few stellar corpses orbiting in a halo of dark matter around a central, supermassive black hole. That mass will grow larger and larger, up until a certain point. Once it’s grown all it can, Hawking radiation will result in the decay of that central black hole, unbinding the last structures of normal matter. In the end, there will be nothing left but a large, massive clump of dark matter in the abyss of empty space.

Need something to look forward to? How about the death of the Milky Way, and the return of the Universe to a cold, empty, unstructured state!