Eight New Quadruple Lenses Aren’t Just Gorgeous, They Reveal Dark Matter’s Temperature
“Ever since astronomers first realized that the Universe required the existence of dark matter to explain the cosmos that we see, we’ve sought to understand its nature. While direct detection efforts have still failed to bear fruit, indirect detection through astronomical observations not only reveal the presence of dark matter, but this novel method of using quadruply lensed quasar systems has given us some very strong, meaningful constraints on just how cold dark matter needs to be.
Dark matter that’s too hot or energetic cannot form structures below a certain scale, and the observations of these ultra-distant, quadruple-lens systems show us that dark matter must form clumps on very small scales after all, consistent with them being born as arbitrarily cold as we can imagine. Dark matter’s not hot, nor can it even be very warm. As more of these systems come in and our instruments go beyond what even Hubble’s capabilities are, we might even discover what cosmologists have long suspected: dark matter must not only be cold today, but it must have been born cold.”
We might not yet know the nature of dark matter, as we’ve never been able to detect the particle responsible for it directly. But we know it clumps and gravitates together, with the exact way it would do so dependent on the amount of kinetic energy it had when it was born relative to its mass. Dark matter could have been extremely hot, such as a scenario where it was made from neutrinos, cold, such as from a very heavy WIMP particle (or a born-super-cold axion), or anywhere in between.
Thanks to a new technique involving quadruple-lens systems, we’ve just learned how cold dark matter needs to be. Get the (beautiful) story today!
Astronomers Find A Galaxy Of Unusual Size (G.O.U.S.), And Discover Why It Exists
“At 800,000 light-years across and with some 4 trillion stars inside, this is one of the largest spiral galaxies ever discovered: a true cosmic outlier. At just 230 million light-years away, it’s also close enough that we can image and identify its globular clusters and star formation rate. The fact that a galaxy this large and massive is so regularly shaped, with such low levels of star formation and so few globular clusters (1600) for its incredible size really does make this a cosmic unicorn.
This galaxy of unusual size really is a first-of-its-kind, and not just for being so beautifully symmetric and quiet, but for growing to this enormous magnitude without a single major disruptive event throughout its history. In all the Universe, there may not be another like it, but the odds are far better that this is just the first discovery of a new type of spiral galaxy: a G.O.U.S.”
How big can a spiral galaxy gets? While most of them are only tens of thousands of light-years across, larger ones like the Milky Way and Andromeda are common, and a small fraction are even bigger. But the newest record-holder, UGC 2885 or Rubin’s galaxy, is truly unusual: it looks like it’s never had a major or even a mid-sized merger before.
How did this galaxy come to exist? Astronomers have cracked the mystery, so go learn all the details about the new cosmic record-holder here!
The Smallest Galaxies Have Off-Kilter Black Holes, But Astronomers Know Why
“Over 100 dwarf galaxies are now known to possess these black holes, with the first verified one discovered in 2011. However, solely finding radio emissions isn’t enough: active black holes and star-formation bursts can create that signal. Researchers led by Dr. Amy Reines just conducted the first large-scale radio survey looking for black holes in dwarf galaxies. Using the Very Large Array, her team surveyed 111 dwarf galaxies, and found 13 of them that showed evidence for massive black holes. Remarkably, approximately half of the black holes were not located at the galaxy’s centers, but were significantly off-kilter.”
When we examine the supermassive black holes we find in the Universe, they’re pretty much always found at the centers of galaxies. However, these are for black holes of millions-to-billions of solar masses and galaxies comparable in mass (or even greater than that) to the Milky Way. But dwarf galaxies, the majority of galaxies in the Universe, are predicted to have much smaller black holes. The first large survey of these galaxies was just undertaken, revealing a population of dwarf galaxies with black holes.
But half of them are located off-center, rather than at the center! Why is that? Astronomers know, and you can too!