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It's Confirmed. M87's Black Hole is Actually Spinning

The supermassive black hole at the heart of M87 was the target of the Event Horizon Telescope, revealing the area around its event horizon for the first time. Although an accretion disk surrounded the black hole, astronomers weren’t sure if the black hole itself was rotating. They imaged the region with radio telescopes and discovered the remnants of polar jets, showing that the black hole’s rotation axis had undergone precession over time. This precession indicates that the black hole is rotating; they’re just not sure how quickly yet.

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The Milky Way's Mass is Much Lower Than We Thought

How massive is the Milky Way? According to a new study using data from ESA’s Gaia spacecraft, less than we thought. A new estimate puts the Milky Way’s mass at 200 billion times the mass of the Sun, which is 4-5 times less than previous estimates that pegged it closer to a trillion solar masses. Using detailed information about millions of stars, astronomers were able to build an extremely accurate rotation curve for the Milky Way and use that to estimate its mass. They found that the rotation of the Milky Way isn’t typical for large spiral galaxies, decreasing its estimated mass.

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It's Official, Antimatter Falls Down in Gravity, Not Up

Since the discovery of antimatter decades ago, particle physicists have wondered if these particles were repulsed by gravity. Einstein predicted that despite having opposite charges to its regular matter counterparts, antimatter should still behave like matter does concerning gravity. This has been tricky to confirm experimentally since it’s hard to make enough antimatter to observe its behavior. Particle physicists have finally pulled it off, using the ALPHA-g experiment at CERN, generating antihydrogen atoms and then dropping them in a 3-meter tall vertical shaft.

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Dark Matter Could Be Annihilating Inside White Dwarfs

Astronomers still don’t know what dark matter is, but one of its characteristics is that it has a small “cross section,” which means that it doesn’t interact with regular matter or itself. However, if it’s possible to trap dark matter in a region dense enough, it might interact and annihilate, releasing gamma radiation. A new paper suggests that astronomers use gamma-ray observatories to scan white dwarf stars to discover whether there’s an excess of radiation coming from them. This might mean there’s dark matter trapped inside, providing more clues to its nature.

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We Can't See the First Stars Yet, but We Can See Their Direct Descendants

The first stars in the Universe were enormous, made of primordial hydrogen and helium from the Big Bang. They lived short lives, exploded as supernovae, and seeded nearby nebulae with heavier elements that began the next generation of stars. Our telescopes aren’t powerful enough to see them yet, but have astronomers found their direct descendants? The metal-poor stars in the galactic halo seem to show the imprints from those first stars and could offer valuable clues about the first stars in the Universe.

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First Contact Could Turn Out Well for Humanity

Most science fiction portrays the first contact between humanity and alien civilizations as a disaster. That’s probably because our history hasn’t turned out so well. But does it have to end poorly for us? A new paper looks at the game theory of first contact. It shows that the rational response to another civilization is to be cautious, with both groups understanding the other before taking decisive action. Communication would be difficult but not impossible. Since we share a physical Universe and have reached a technology level that allows us to detect each other, we could assume some of their characteristics in advance.

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Polar Ring Galaxies Are Bizarre and Rare. Astronomers Just Found Two More

Many galaxies resemble the Milky Way, with billions of stars organized into a rotating, rotating spiral. There are other irregular galaxies and giant elliptical galaxies with less defined structures, but one of the most bizarre types of galaxies is called “polar rings.” In these galaxies, the central core is surrounded by a ring of gas and a star perpendicular to the central spiral disk. It’s believed they’re formed when a larger galaxy swallows a smaller one, extruding its stars into a ring. A recent survey revealed two previously unknown polar ring galaxies, which could be more common than previously believed.

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An Ambitious New Technology Might be Needed to See Other Earths

NASA and its partners are starting to develop plans for the Habitable Worlds Observatory flagship mission that’s due to launch in the late 2030s or 2040s. Its primary goal will be to observe other Earth-sized worlds orbiting Sun-like stars within the habitable zone. To do this requires blocking the light from the star with an internal coronagraph and a separate starshield. A new paper suggests that NASA should consider a “photonic chronograph” that could be twice as effective in revealing faint planets beside bright stars.

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The Milky Way's Disk is Warped. Is That Because our Dark Matter Halo is Tilted?

Astronomers have measured the Milky Way’s shape and found that the disk is warped and not a flat spiral like many of the galaxies we see in the Universe. It was assumed a collision with another galaxy in the ancient past caused this warping. Observations have shown that the galactic stellar halo is tilted concerning the galactic plane, and a new theory proposes that the dark matter halo is tilted, too. This tilt might be torquing the galaxy, causing the warp that astronomers have observed.