The gravitational waltz of the Milky Way’s satellites

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I’ve started contributing to the Forbes Science page again! This is my first new contribution, relating to the second data release from the Gaia survey telescope. (And if I can be shameless: Forbes pays according to traffic, so the more of you who share and visit and read my stuff, the better they pay me. Ahem.)

Plotting The Three-Dimensional Dance Of Galaxies

A map of the Milky Way’s satellite galaxies, globular clusters, and other objects in orbit. [Credit: ESA/Gaia]

For Forbes:

The European Space Agency’s Gaia telescope is designed to map the position and speed of a billion stars in the Milky Way and its neighboring galaxies. In fact, some of those galaxies are satellites, which whirl around our home galaxy in a complicated dance. Part of Gaia’s mission is to help us understand that dance.

Many of these satellite galaxies actually orbit inside the halo of the mysterious, invisible dark matter that makes up most of the Milky Way’s mass. For that reason, the dance of the satellites tells us about the structure of the Milky Way, along with the shared history and evolution of all the galaxies involved. The Gaia space telescope’s second data release from last week allowed astronomers to map out the positions and motion of stars inside eleven satellite galaxies, along with other star clusters. The result: new estimate on the mass of the Milky Way, and a fully three-dimensional map of nearly 90 objects in orbit around our galaxy.

[Read the rest at Forbes]


Forging dark matter in the Big Bang

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The origins of dark matter

Theorists think dark matter was forged in the hot aftermath of the Big Bang

For Symmetry Magazine:

Transitions are everywhere we look. Water freezes, melts, or boils; chemical bonds break and form to make new substances out of different arrangements of atoms. The universe itself went through major transitions in early times. New particles were created and destroyed continually until things cooled enough to let them survive.

Those particles include ones we know about, such as the Higgs boson or the top quark. But they could also include dark matter, invisible particles which we presently know only because of their gravitational effects.

In cosmic terms, dark matter particles could be a “thermal relic,” forged in the hot early universe and then left behind during the transitions to more moderate later eras. One of these transitions, known as “freeze-out,” changed the nature of the whole universe. [Read the rest at Symmetry Magazine]

Finding all the matter in the cosmos — even the invisible stuff

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“Weak Lensing” Helps Astronomers Map the Mass of the Universe

By making galaxies a little bit brighter, it points the way to elusive galaxies and lets us detect that most mysterious of substances: dark matter

For Smithsonian Magazine:

In ordinary visible light, this cluster of galaxies doesn’t look like much. There are bigger clusters with larger and more dramatic-looking galaxies in them. But there’s more to this image than galaxies, even in visible light. The gravity from the cluster magnifies and distorts light passing near it, and mapping that distortion reveals something about a substance ordinarily hidden from us: dark matter.

This collection of galaxies is famously called the “Bullet Cluster,” and the dark matter inside it was detected through a method called “weak gravitational lensing.” By tracking distortions in light as it passes through the cluster, astronomers can create a sort of topographical map of the mass in the cluster, where the “hills” are places of strong gravity and “valleys” are places of weak gravity. The reason dark matter—the mysterious substance that makes up most of the mass in the universe—is so hard to study is because it doesn’t emit or absorb light. But it does have gravity, and thus it shows up in a topographical map of this kind.

The Bullet Cluster is one of the best places to see the effects of dark matter, but it’s only one object. Much of the real power of weak gravitational lensing involves looking at thousands or millions of galaxies covering large patches of the sky. [Read the rest at Smithsonian Magazine]

A multitude of faint and fluffy galaxies

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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…]

Why do some want to modify general relativity?

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And yes, I did refer to MOND as “a fungus in the basement of astronomy”.

Do We Need to Rewrite General Relativity?

For NOVA “The Nature of Reality”:

General relativity, the theory of gravity Albert Einstein published 100 years ago, is one of the most successful theories we have. It has passed every experimental test; every observation from astronomy is consistent with its predictions. Physicists and astronomers have used the theory to understand the behavior of binary pulsars, predict the black holes we now know pepper every galaxy, and obtain deep insights into the structure of the entire universe.

Yet most researchers think general relativity is wrong.

To be more precise: most believe it is incomplete. After all, the other forces of nature are governed by quantum physics; gravity alone has stubbornly resisted a quantum description. Meanwhile, a small but vocal group of researchers thinks that phenomena such as dark matter are actually failures of general relativity, requiring us to look at alternative ideas. [Read the rest at NOVA…]

The dinosaur-killing dark matter of DOOM!

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A few weeks ago, several news outlets ran stories based on a press release, in which a researcher claimed that dense clumps of dark matter could be responsible for the extinction of dinosaurs. I found this claim dubious, based on what we know about dark matter. Here’s my response.

Did Dark Matter Doom the Dinosaurs?

From Slate:

he history of life on Earth is marked by occasional mass extinctions, events wiping out huge numbers of species. The most famous of these killed off all the dinosaurs (or at least those that hadn’t evolved into birds) 65 million years ago. But the mass extinction that ended the Permian period 250 million years ago was even more dramatic, killing off 90 percent of all species in an astonishingly short amount of time. As yet, the cause of this devastation is unexplained.

Mass extinctions have happened at least five times. (A sixth great extinction currently in progress, but that’s an anomaly because humans are responsible.) Some researchers have tried to figure out whether they’re periodic, recurring after specific time intervals. If they truly do repeat regularly, maybe there’s a common cause for them. [read more on]

Weird X-Rays Spur Speculation about Dark Matter Detection

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Weird X-Rays Spur Speculation about Dark Matter Detection

From Scientific American:

Many major discoveries in astronomy began with an unexplained signal: pulsars, quasars and the cosmic microwave background are just three out of many examples. When astronomers recently discovered x-rays with no obvious origin, it sparked an exciting hypothesis. Maybe this is a sign of dark matter, the invisible substance making up about 85 percent of all the matter in the universe. If so, it hints that the identity of the particles is different than the prevailing models predict.

The anomalous x-rays, spotted by the European Space Agency’s orbiting XMM–Newton telescope, originate from two different sources: the Andromeda Galaxy and the Perseus cluster of galaxies. The challenge is to determine what created those x-rays, as described in a study published last month in Physical Review Letters. (See also an earlier study published in The Astrophysical Journal.) The signal is real but weak and astronomers must now determine whether it is extraordinary or has a mundane explanation. If that can be done, they can set about the work of identifying what kind of dark matter might be responsible. [Read more at Scientific American ]