Archive for the ‘astronomy’ Category

Sonic black holes produce “Hawking radiation,” may confirm famous theory

May 30th, 2019
Simulated view of a black hole in front of the Large Magellanic Cloud.

Enlarge / Simulated view of a black hole in front of the Large Magellanic Cloud. (credit: Wikimedia Commons/Alain r)

Israeli physicists think they have confirmed one of the late Stephen Hawking's most famous predictions by creating the sonic equivalent of a black hole out of an exotic superfluid of ultra-cold atoms. Jeff Steinhauer and colleagues at the Israel Institute of Technology (Technion) described these intriguing experimental results in a new paper in Nature.

The standard description of a black hole is an object with such a strong gravitational force that light can't even escape once it moves behind a point of no return known as the event horizon. But in the 1970s, Hawking demonstrated that—theoretically, at least—black holes should emit tiny amounts of radiation and gradually evaporate over time.

Blame the intricacies of quantum mechanics for this Hawking radiation. From a quantum perspective, the vacuum of space continually produces pairs of virtual particles (matter and antimatter) that pop into existence and just as quickly annihilate away. Hawking proposed that a virtual particle pair, if it popped up at the event horizon of a black hole, might have different fates: one might fall in, but the other could escape, making it seem as if the black hole were emitting radiation. The black hole would lose a bit of its mass in the process. The bigger the black hole, the longer it takes to evaporate. (Mini-black holes the size of a subatomic particle would wink out of existence almost instantaneously.)

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Posted in analogue black holes, astronomy, black holes, Hawking radiation, Physics, quantum simulations, science | Comments (0)

Impact that formed the Moon might have splashed into Earth’s magma ocean

April 30th, 2019
Image of a small object smashing in to a cutaway off the Earth.

Enlarge / An early version of the collision model, showing a head-on impact.

The Earth and its moon are unique in our Solar System. Earth is the only rocky planet with a large moon, and only the dwarf planet Pluto has a moon that's so similar in size to its host planet. The Moon is also remarkably similar to the Earth in terms of its composition, suggesting they formed from the same pool of material instead of the Moon forming elsewhere and having been captured.

This collection of properties led to a number of ideas about how the Moon formed, all of which failed to fit the data in various ways. Eventually, however, scientists came up with an idea that seemed to get most of the big picture right: a collision between the Earth and a Mars-sized object happened early in the Solar System's history, creating a cloud of debris that coalesced into the Moon.

While that got the major features of our two-body system right, there were still some subtle differences that weren't resolved by the impact model. Now, a team of Japanese researchers say that there's a way to tidy up some of these loose ends: having the impact take place while the Earth was covered in a molten magma ocean.

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Posted in astronomy, Earth, geology, moon, planetary science, science | Comments (0)

What Starry Night has in common with gassy clouds where stars are born

April 23rd, 2019
The bold blue and yellow swirls of Vincent van Gogh's <em>Starry Night</em> (1889) share turbulent properties with the molecular clouds that give birth to stars.

Enlarge / The bold blue and yellow swirls of Vincent van Gogh's Starry Night (1889) share turbulent properties with the molecular clouds that give birth to stars. (credit: Museum of Modern Art/Public domain)

In 2004, NASA published an image by the Hubble Space Telescope of turbulent eddies of dusty clouds moving around a supergiant star. The agency noted that this "light echo" was reminiscent of Vincent van Gogh's masterpiece, Starry Night. Now, two Australian graduate students have mathematically analyzed the painting and concluded it shares the same turbulent features as molecular clouds (where literal stars are born). They described their work in a paper posted to the physics arXiv.

The notion that van Gogh's often troubled life was reflected in his work is not especially new. In a 2014 TED-Ed talk, Natalya St. Clair, a research associate at the Concord Consortium and coauthor of The Art of Mental Calculation, used Starry Night (1889) to illuminate the concept of turbulence in a flowing fluid. In particular, she talked about how van Gogh's technique allowed him (and other Impressionist painters) to represent the movement of light across water or in the twinkling of stars. We see this as a kind of shimmering effect, because the eye is more sensitive to changes in the intensity of light (a property called luminance) than to changes in color.

In physics, turbulence relates to strong, sudden movements within air or water, usually marked by eddies and vortices. Physicists have struggled for centuries to mathematically describe turbulence. It's still one of the great remaining challenges in the field. But a Russian physicist named Andrei Kolmogorov made considerable progress in the 1940s when he predicted there would be a mathematical connection (now known as Kolmogorov scaling) between how a flow's speed fluctuates over time and the rate at which it loses energy as friction.

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Posted in art, astronomy, astrophysics, fluid dynamics, Gaming & Culture, Physics, science, starry night, turbulence, Vincent van Gogh | Comments (0)

We now have images of the environment at a black hole’s event horizon

April 10th, 2019
The first image of the environment around a black hole. As a matter of fact, it's not all dark.

Enlarge / The first image of the environment around a black hole. As a matter of fact, it's not all dark. (credit: National Science Foundation)

Two years ago, telescopes around the world turned their attention to two supermassive black holes. Now, after a massive computational effort, their data has been combined in a way that allowed them to function as a single, Earth-sized telescope. The results are an unprecedented glimpse of the environment around supermassive black holes, and confirm that relativity still works under the most extreme gravitational forces.

The black hole in question is a supermassive one at the center of the galaxy M87, 55 million light years away, an active galaxy where the black hole is feeding on matter and ejecting jets of material. The image is made from photons that were temporarily trapped in orbit around the black hole. Here, the intense gravity causes matter—and even space itself—to move at approximately the speed of light. The eventual escape of these photons causes a bright ring to appear around the black hole itself, with the details of the ring reflecting the physics of the black hole itself.

A monster

At a press conference this morning, Avery Broderick of the Perimeter Institute described what the images tell us about the black hole itself. One key finding is that the object is a black hole, at least as we've understood black holes using relativity. It does not have any visible surface, and the "shadow" of light it creates is circular within the limits of our observations. We can also tell that it spins clockwise. All of the properties we can infer from these images are consistent with relativity. "I was a little stunned that it matched the predictions we made so well," said Broderick.

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Posted in astronomy, black holes, general relativity, science | Comments (0)

One night of telescope time rules out black hole/dark matter idea

April 6th, 2019
19th-century etching of a telescope in use.

Enlarge / 19th-century etching of a telescope in use. (credit: Fondo Antiguo de la Biblioteca de la Universidad de Sevilla / Flickr)

Much of the Universe behaves as if there's more matter there than we can see. Dark matter explains this by positing that there's matter present that we can't see, and evidence has piled up in favor of this idea. In contrast, evidence for the identify of dark matter has behaved in an opposite manner: every thing we've done to look for it has come up empty.

The latest bit of emptiness was published this week, and it seemingly puts an end to one of the possible remaining explanations for dark matter: black holes that formed shortly after the Big Bang and have been structuring the Universe ever since. While earlier studies have seemingly ruled out larger versions of these primordial black holes, the new study closes the window on anything more massive than a large asteroid. And it was all accomplished with just a single night of telescope time.

From the dawn of time

Black holes would seemingly make fantastic candidates for dark matter, given that they're black and thus difficult to detect. But there's a number of reasons they don't work especially well. For one, while light may not escape a black hole, it's often produced in prodigious amounts by the material just outside a black hole. So it's not clear whether large numbers of black holes could somehow go undetected.

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Posted in astronomy, black holes, Dark Matter, science | Comments (0)

Hayabusa2 finds that its destination is also a very dark rubble pile

March 19th, 2019
Greyscalle image of a dusty field of rocks.

Enlarge / A sense of the phenomenal resolution at which we can explore the asteroid Ryugu. (credit: JAXA)

Asteroids can tell critical stories about the birth of our Solar System and the processes that produced its planets. In some cases, they are time capsules for the planetesimals that went on to form our planets. In others, they've been through multiple rounds of catastrophic collisions and reformation, providing testimony of the violent processes that built our current Solar System. But figuring out what they tell us has been difficult, because their small size and generally large distance from Earth make them difficult to study using telescopes. And the bits and pieces we have been able to study directly have been altered by the process of plunging from space through the Earth's atmosphere.

All that's on the verge of changing in the near future, as we have not one but two missions that will return samples from asteroids over the next couple of years. In the case of JAXA's Hayabusa2 mission, the first sample retrieval has already taken place, while NASA's OSIRIS-REx arrived at its destination more recently. But since arriving, both probes have been studying the mini-worlds they were sent to, and the first results of those studies are now in.

Today, Nature and Science are releasing a large collection of papers that describe the initial observations of the two asteroids that these missions have targeted. The bodies have turned out to be remarkably similar, as you can see by visiting our Bennu coverage and then comparing it with what we now know about Ryugu, described below.

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Posted in asteroids, astronomy, hyabusa2, JAXA, planetary science, science | Comments (0)

This medieval astrolabe is officially world’s oldest known such instrument

March 17th, 2019
Left: A laser imaging scan of the so-called Sodre astrolabe, recovered from the wreck of a Portuguese Armada ship. Right: The astrolabe is believed to have beeb made between 1496 and 1501.

Enlarge / Left: A laser imaging scan of the so-called Sodre astrolabe, recovered from the wreck of a Portuguese Armada ship. Right: The astrolabe is believed to have beeb made between 1496 and 1501. (credit: David Mearns/University of Warwick)

A mariner's astrolabe recovered from the wreck of one of Portuguese explorer Vasco da Gama's ships is now officially the oldest known such artifact, according to a new paper in the International Journal of Nautical Archaeology. It's even going into the Guinness Book of world records, along with the ship's bell, now that both have been independently verified as the oldest of their kind in the world.

Key distinction: this is the oldest known mariner's astrolabe. Astrolabes are actually very ancient instruments—possibly dating as far back as the Second Century, B.C.—for determining the time and position of the stars in the sky by measuring a celestial body's altitude above the horizon. They were mostly used for astronomical studies,  although they also proved useful for navigation on land. Navigating at sea was a bit more problematic, unless the waters were calm.

The development of a mariner's astrolabe—a simple ring marked in degrees for measuring celestial altitudes—helped solve that problem. It was eventually replaced by the invention of the sextant in the18th century, which was much more precise for seafaring navigation. Mariner's astrolabes are among the most prized artifacts recovered from shipwrecks; only 108 are currently catalogued worldwide.

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Posted in astrolabes, astronomy, history of science, navigation, science, shipwrecks | Comments (0)

The perils of upgrading a particle detector buried in Antarctic ice

March 4th, 2019
Image of people working on electronics in a snow trench.

Enlarge / IceCube scientist Delia Tosi (right) and engineer Perry Sandstrom (left) install a prototype power and communications junction box at the South Pole. (credit: John Kelley / National Science Foundation)

The IceCube neutrino detector was an audacious design. The Super Kamiokande detector had shown that a huge mass of water could act as an effective particle detector. But that involved a giant tank built in a deep mine. IceCube would rely on a massive volume of water, but one that was put in place by nature: the Antarctic ice cap. That poses a large collection of challenges, from how to find hardware that can hold up to being buried in the ice to how do you get the data back out and someplace useful.

The success of the detector—it's given us insight into some of the highest-energy events in the Universe—indicates that these challenges have been overcome. But now IceCube is expanding, with an upgrade in the works and a much larger next-generation detector being planned, posing a new set of challenges. To get a perspective on this one-of-a-kind detector, we talked with John Kelly, IceCube's detector operations manager and self-proclaimed Ars reader.

Lighting up the ice

While neutrinos only rarely interact with other matter—it's estimated that you need about a lightyear of lead to stop them—there are a lot of neutrinos around, and IceCube monitors a lot of matter. During construction, teams melted holes deep into the ice, allowing them to run long strings of photodetectors over two kilometers deep into the ice. Collectively, they monitor over a cubic kilometer of it.

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Posted in Antarctica, astronomy, IceCube, neutrinos, particle physics, science | Comments (0)

Craters on Pluto suggest Kuiper Belt ate its smaller bodies

March 2nd, 2019
Image of craters on a moon.

Enlarge / A view of Vulcan Planitia's craters on Charon. (credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/K. Singer)

What did the earliest bodies in our Solar System look like, and what was their fate? It's difficult to tell, because it's not clear that there are any of them left. Lots of the earliest material was swept up into the planets. Many of the smaller bodies that remained are products of multiple collisions and have perhaps formed and re-formed multiple times—some are little more than rubble piles barely held together by gravity.

Without some knowledge of what these bodies looked like, then, it's difficult to determine whether our models of the physics of the early Solar System are right and whether similar processes are likely to be in play in exosolar systems.

Now, some researchers have found a way to infer the sizes of objects present in the early Solar System: looking at the craters they left behind when they smashed into Pluto and Charon. The results suggest a shortage of objects smaller than 2km in diameter and suggest that much of the material in the Kuiper Belt was quickly swept up into larger objects, which somehow avoided smashing into each other and liberating a new generation of smaller fragments.

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Posted in astronomy, Charon, craters, Kuiper belt, New Horizons, planetary science, Pluto, science | Comments (0)

Hubble images show a Neptune moon that may have been repeatedly reborn

February 20th, 2019
Image of a small, rocky body with Neptune in the background.

Enlarge / An artist's concept of the tiny moon Hippocamp. (credit: NASA, ESA, and J. Olmsted)

As the Voyager probes moved through the outer Solar System, they compiled a massive record of discovery. Among the newly found objects and phenomena were a large collection of small moons orbiting Jupiter, Saturn, Uranus, and Neptune. Most of these were beyond the ability of Earth-based hardware to image at the time—we actually had to be there to see them.

Since then, however, improvements in ground-based optics and the existence of the Hubble Space Telescope have enabled us to find a few small bodies that had been missed by the Voyagers, as well as other small objects elsewhere in the Solar System, such as the Kuiper Belt object recently visited by New Horizons. Now, researchers have found a way to use advances in computation to increase what we can do with imaging even further, spotting a tiny new moon at Neptune and possibly spotting another for the first time since Voyager 2 was there.

Finding moons

Given that Neptune has been visited by Voyager 2 and imaged frequently since then, any moons we haven't already spotted are going to be pretty hard to see, presumably because they're some combination of small and/or dim. The simplest way to see them is to increase the exposure time, allowing more opportunity for dim signals to emerge from the noise. This method won't work if there's a bright object nearby, which isn't so much of a problem with the outer planets.

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Posted in astronomy, Hubble, Neptune, planetary science, science | Comments (0)