Could The Milky Way Be More Massive Than Andromeda?
“The Milky Way is home to the Sun, our Solar System, and hundreds of billions of stars beyond that. Yet unlike all the other galaxies out there — in our Local Group and in the Universe beyond — we have no good way to view our own galaxy from our position within it. As a result, the full extent of our galaxy, including its total size, mass, matter content, and number of stars, remains mysterious to modern astronomers.
We’ve long looked at the galaxies surrounding our local neighborhood in space and compared ourselves to them. Although there may be more than 60 galaxies present within the Local Group, two of them dominate in every way imaginable: ourselves and Andromeda. We are the two largest, most massive galaxies around, with more stars than all the others combined. But which one is bigger? Long thought to be Andromeda, we’re now finding out the Milky Way might have a chance at being number one.”
It’s 2019, and we still don’t know how massive the Milky Way is, or even whether we’re the most massive galaxy in the Local Group or not. It’s a lot like measuring your eye color: looking out at everyone else, it’s easy to see what color their eyes are. But if you didn’t have a reflection, photograph, or the observations of others, how would you know your own eye color? Well, being trapped within the Milky Way makes measurements notoriously difficult, and we’re only now figuring out how to overcome that obstacle.
It’s not only possible, but even likely that the Milky Way, despite having fewer stars occupying less volume than Andromeda’s, is the most massive galaxy in the Local Group. Come get the full story.
Hubble: Andromeda Is Big, Massive, And Full Of The Stars Our Milky Way Is Missing
“The low-density, outer halo contains stars just as ancient as the Milky Way’s oldest: 13+ billion years of age. Andromeda has stellar streams populating that halo, with a third of those stars just 6-8 billion years old.
This means a major act of galactic cannibalism recently occurred.”
Every few years, a new study comes out claiming that the Milky Way may rival the Andromeda galaxy for the status of largest within our local group. Nonsense! Andromeda is practically double the diameter, contains anywhere from 2.5 to 5 times as many stars, and now there’s evidence that it gobbled up a number of massive galaxies relatively recently. Not only does it have stars just as old as the oldest we’ve ever found in the Milky Way, but we now have evidence that, 6-8 billion years ago, it devoured a large member of our local group entirely, with about a third of Andromeda’s halo stars having formed at around that time. When the Milky Way-Andromeda merger finally comes, there can be no doubt that the remnants of Andromeda will dominate whatever’s left.
Come see an astounding collection of images of our Local Group’s biggest, most massive galaxy, and get a window into what #1 in the Local Group looks like!
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!
The Largest Black Hole Merger Of All-Time Is Coming, And Soon
“Over in Andromeda, the nearest large galaxy to the Milky Way, a number of unusual systems have been found.
One of them, J0045+41, was originally thought to be two stars orbiting one another with a period of just 80 days.
When additional observations were taken in the X-ray, they revealed a surprise: J0045+41 weren’t stars at all.”
When you look at any narrow region of the sky, you don’t simply see what’s in front of you. Rather, you see everything along your line-of-sight, as far as your observing power can take you. In the case of the Panchromatic Hubble Andromeda Treasury, where hundreds of millions of stars were captured in impressive fashion, background objects thousands of times as distant can also be seen. One of them, J0045+41, was originally thought to be a binary star system that was quite tight: with just an 80 day orbital period. Follow-up observations in the X-ray, however, revealed that it wasn’t a binary star system after all, but an ultra-distant supermassive black hole pair, destined to merge in as little as 350 years. If we build the right observatory in space, we’ll be able to observe the entire inspiral-and-merger process for as long as we like!
Come get the full story, and some incredible pictures and visuals, on today’s Mostly Mute Monday!
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!
This great photo of Andromeda was taken with a Nikon d90 and a Tal100 telescope, five minute exposure and 800 ISO, edited in lightroom.
Photo taken by Diego Perojil