Tag Archives: galaxies

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Om nom nom: a black hole ate a star and left crumbs for us to see

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And if I can be shameless: Forbes pays according to traffic, so the more of you who click on the link below and read my stuff, the better they pay me. Ahem.

A Black Hole Ate A Star And Left Crumbs Of Light For Astronomers To Discover

colliding galaxies Arp 299

The colliding galaxies Arp 299, as seen in visible light (the background) and X-rays (red, green, and blue foreground). [Credit: NASA, JPL-Caltech, GSFC, Hubble, NuSTAR]

For Forbes:

Astronomers captured the last moments of an unlucky star that got too close to a black hole. However, they didn’t know that’s what we were seeing right away, because the whole scene of carnage was hidden by clouds of gas and dust. Now, with multiple types of observations and more than ten years of data, we have new insights into the way black holes shred stars, as reported in a new paper in Science.

Black holes, like Cookie Monster, are notoriously messy eaters. That’s good for astronomers, though, because the cosmic crumbs a black hole spills during its meal emit a lot of light. If a star gets too close to a black hole, the gravity tears it to pieces in an act known as “tidal disruption”, but only part of the star’s material actually falls in. (This is a more extreme version of the same forces that raise tides on Earth, and which destroyed a small moon to create Saturn’s rings.) The rest of the star gets channeled into a powerful jet that streams away from the black hole back into space.

[Read the rest at Forbes…]

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A multitude of faint and fluffy galaxies

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

Scientists Discover Hundreds of Hidden Galaxies

The new type of faint, fluffy galaxy might help resolve a cosmological conundrum

For The Daily Beast:

When we think of galaxies, we tend to focus on the beautiful spirals, like the Milky Way, or possibly the huge elliptical galaxies. However, we know that a lot of galaxies are small, and those are harder to spot. In fact, astronomers have observed far fewer low-mass galaxies than predicted by theory, which has been a puzzle and a problem.

A new discovery might help with the answer. Astronomers using the Subaru telescope in Hawaii found 854 nearly invisible galaxies in the Coma Cluster. These hidden objects are very large—some are roughly the size of the Milky Way—but extremely low density. This new census is a notable increase in the population of the Coma Cluster, which is already a large galaxy cluster. It’s likely that other galaxy clusters could be hiding fluffy faint galaxies too. [Read more in The Daily Beast…]

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How did the biggest black holes form?

X-ray image of two black holes in the galaxy NGC 6240. Binary systems like this are possibly the origin of the most massive black holes in the cosmos. [Credit: NASA/CXC/MPE/S.Komossa et al. ]

X-ray image of two black holes in the galaxy NGC 6240. Binary systems like this are possibly the origin of the most massive black holes in the cosmos. [Credit: NASA/CXC/MPE/S.Komossa et al.]

The most massive known object in the cosmos is the black hole at the center of M87, a huge galaxy in the Virgo Cluster. While most large galaxies (including the Milky Way) harbor supermassive black holes, the very largest are interesting. That’s because galaxies and their black holes seem to share a history, based on the relationship between the mass of the black hole and the mass of the galaxy’s central region. Since large galaxies grew by devouring smaller galaxies, or by two galaxies merging into a larger one, it’s very likely the biggest black holes followed a similar process. My latest piece for Nautilus examines how this process might have taken place, and what it could reveal about the black holes themselves.

Earth emits gravitational waves as it orbits the Sun, though the amount of energy lost is imperceptible over the lifetime of the Solar System. Binary black holes are a different matter: Once they are relatively close, they shed a tremendous amount of energy, bringing them closer together with each orbit. (Binary black stars are thought to emit more gravitational energy as they merge than regular stars emit in the form of UV, IR, and visible light over their entire lifetimes of billions of years.) Eventually their event horizons will touch, and the system emits a lot more gravitational waves in a phase known as “ring-down,” as the lumpy, uneven merged mass becomes a smooth, perfectly symmetrical black hole. [Read more…]

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A quasar (the bright circle at the image center) is illuminating a cosmic filament, marked out in blue. [Credit: S. Cantalupo]

A quasar (the bright circle at the image center) is illuminating a cosmic filament, marked out in blue. [Credit: S. Cantalupo]

Astronomers have identified a filament in the cosmic web, which is the pattern formed by dark matter. That web in turn dictates the distribution of galaxies, since the dark matter attracts ordinary matter — atoms — through its gravity. However, it’s hard to spot the filaments connecting the different halos of dark matter, because they are far less massive and contain less gas than galaxies. The trick in this new study was to spot the faint glow of gas as it was lit up by a quasar: a bright energetic black hole in a nearby galaxy.

Sebastiano Cantapulo and colleagues observed the light emitted by the filament’s gas as it glowed under bombardment from a quasar, a powerful jet of particles propelled from a massive black hole. However, the researchers also found at least ten times more gas than expected from cosmological simulations, which suggests that there may be more gas between galaxies than models predict. [Read more….]

A glowing filament shows us where the dark matter hides

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Early galaxies: live large, die big, burn bright

How did the biggest galaxies form? Based on the ages of stars inhabiting them, the largest elliptical galaxies — those kind of boring egg-shaped clouds of stars with no pretty spiral arms — formed fairly early in the history of the Universe. While smaller elliptical galaxies likely are the modern version of submillimeter bright galaxies (SBGs), star-forming structures visible from the early cosmos, astronomers have failed to identify the progenitors of the largest galaxies. However, a new paper might have the answer: the authors caught a pair of early galaxies right before they collided, after which they likely merged into one.

Where one galaxy is insufficient, two may do instead. A new set of observations caught two bright elliptical galaxies right before the act of merging into one that would have a combined mass large enough to make the equivalent of 400 billion Suns. Hai Fu and colleagues determined that these galaxies collided more than 10 billion years ago and that the merger was driving extremely rapid star formation, at least ten times the rate seen in ordinary galaxies. Based on these observations, the researchers concluded that such collisions could be responsible for the birth of the largest galaxies, allowing for most of them to finish forming by 9.5 billion years ago. [Read more…]

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Green Peas were all my joy, galaxies were my delight

Most galaxies are somewhat red or blue in appearance, depending on the populations of stars that comprise them. However, citizen scientists working with the GalaxyZoo project identified a previously unknown type of galaxy: Green Peas, so named because they are small and green. The color comes from ionized oxygen, a particular form of emission that only happens under unusual conditions. A new study shows that Green Peas could resemble a kind of early galaxy responsible for reionization: the breakdown of atoms due to aggressive star formation when the Universe was young.

A new paper by A. E. Jaskot and M. S. Oey argues that galaxies much like the Green Peas could be responsible for the reionizing radiation. They analyzed the light emissions from the galaxies, and determined that their gas is thinner than in typical star-forming galaxies, which could allow more ultraviolet light into intergalactic space. The researchers also found signs in a few Green Peas of extremely massive stars, the ones most responsible for ionizing radiation. [Read more…]

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Our local group of galaxies—known imaginatively as the Local Group—has two huge galaxies: the Milky Way and M31, also known as the Andromeda Galaxy. Both of these galaxies are large enough to have a number of satellites, including the substantial Magellanic Clouds and M33 (Triangulum Galaxy). However, most satellites are dwarf galaxies, very faint and relatively low mass. As a result, a moderately complete census of satellites has proven difficult even for the Milky Way, but what recent observations have found is surprising. In both cases, a number of the satellite galaxies orbit in a single plane, and at least in the case of Andromeda, they orbit in the same direction.

The Pan-Andromeda Archaeological Survey (featuring the diverting acronym PAndAS) was established to provide a high-resolution, large-scale panorama of M31 and its environs. 27 dwarf galaxies that can be unambiguously associated with Andromeda lie within the PAndAS survey region. The astronomers measured the distances and velocities of each of these galaxies, yielding a three-dimensional and dynamical view of the M31 system.

They found 15 of those satellites were arranged along a relatively thin arc from the perspective of Earth, meaning they lie close to a single plane. Further analysis revealed 13 of the 15 galaxies were also moving in a coherent pattern: those “north” of Andromeda were moving away from us, while those “south” were traveling toward us. That indicates a clear rotational pattern; the authors estimated only a 1.4 percent probability of motion like this being random chance. [Read more…]

Why do half of Andromeda’s satellite galaxies orbit in a plane?