Category Archives: Ars Technica

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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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Gravity is a universally attractive force, at least as far as we can tell. However, some physicists have posited that antimatter behaves the opposite way, as though they have negative mass. Testing that hypothesis is remarkably hard, though: antimatter particles annihilate with their regular matter partners if they encounter each other (at low speeds at least), and gravity is by far the weakest force in the Universe. As a result, we can’t make a big weight out of antimatter and drop it. So, researchers at CERN have proposed another way, using the existing ALPHA experiment designed to trap anti-hydrogen. While preliminary results can’t answer whether antimatter possesses antigravity, the experiment itself is promising.

How deep does the asymmetry between matter and antimatter go? Each type of particle (electrons, protons, etc.) have antimatter partners: positrons, antiprotons, and so forth. These antiparticles have an opposite electric charge (unless they’re neutral), but otherwise behave much like their matter counterparts. But one interesting question remains unanswered: does antimatter possess antigravity, experiencing a repulsive force when matter experiences attraction? And, even if antimatter experiences plain old gravity, does it behave in exactly the same way as matter does?

Researchers from the ALPHA experiment at CERN realized their antihydrogen trap could help answer that question. [Read more...]

What goes up, must come down…except maybe antimatter

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General relativity holds up under extreme gravity test

The general theory of relativity is the reigning champion of gravitational theories: it’s withstood tests in the Solar System, near black holes, and in binary systems. Most recently, astronomers performed detailed observations of a pulsar-white dwarf binary system, which provided an exquisite example of general relativity in action. Pulsars and white dwarfs are both the remnants of stars, but pulsars in particular are interesting: they pack the mass of a star into a sphere about 20 kilometers across. That means the gravity at the surface of a pulsar is extreme, so when one is in a binary system, it provides a laboratory for measuring strong gravitational effects.

The pulsar itself was interesting because of its relatively high mass: about 2.0 times that of the Sun (most observed pulsars are about 1.4 times more massive). Unlike more mundane objects, pulsar size doesn’t grow with mass; according to some models, a higher mass pulsar may actually be smaller than one with lower mass. As a result, the gravity at the surface of PSR J0348+0432 is far more intense than at a lower-mass counterpart, providing a laboratory for testing general relativity (GR). The gravitational intensity near PSR J0348+0432 is about twice that of other pulsars in binary systems, creating a more extreme environment than previously measured. [Read more...]

Also, let the record show: it’s possible to write an article about testing general relativity without mentioning Einstein, much less making the story about “proving him right” (or wrong).

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My media badge from the aborted Antares rocket test launch.

My media badge from the aborted Antares rocket test launch.

Most major American rocket launches have been from Florida, which means I’ve never had a real opportunity to see one. However, NASA’s Wallops Flight Facility is beginning to host orbital rocket launches, in collaboration with the private company Mid-Atlantic Regional Spaceport (MARS). (Historically, Wallops has launched suborbital rockets and balloons.) So, I trekked over to Wallops Island, Virginia to watch the test launch of the new Antares rocket from Orbital Sciences Corporation. Unfortunately, that test was aborted during the countdown, but I managed to write a few pieces about the experience anyway. (Antares successfully reached orbit on Sunday, so all was well that ended well.)

I went to a rocket test launch, and all I got was this stupid name tag

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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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White dwarfs are the remnants of the cores of stars like our Sun. They have the mass of a star packed into the volume of Earth, but when they die, their light can be detected across the observable Universe. Researchers using the Hubble Space Telescope identified the farthest white dwarf supernova yet seen, one which exploded more than 10 billion years ago.

Only 8 white dwarf supernovas have been identified farther than 9 billion light-years away. (Some core-collapse supernovas, which are the explosions of very massive stars, have been seen farther than Supernova Wilson.) Since all such explosions happen in a similar way, cosmologists use them to measure the expansion rate of the Universe. [Read more...]

I gotta say, though: this supernova was nicknamed “Woodrow Wilson”, which kind of bugs me. Wilson was a war president, which means we Americans tend to give him a pass on a lot of things, but both his foreign and domestic policies reeked of racism. He worked against racial equality at home and abroad, stamping on egalitarian movements in the League of Nations and segregating the Federal Government. (The previous Republican administrations, for all their faults, had been making efforts to give African-Americans a voice after the Civil War.) Anyway, that’s mostly beside the point. If you want to read about a supernova named for someone whose work I do admire (prickly though he was), see my post about Supernova Mingus.

Death of a white dwarf, 10 billion years later

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Let the record show: I am the first writer for Ars Technica to use the phrase “om nom nom”. Astronomers caught a supermassive black hole in the act of disrupting and devouring part of a large planet or small brown dwarf (a starlike object that isn’t massive enough for nuclear fusion). The giveaway was a burst of gamma ray light, which peaked then faded slowly over time, very different from usual black hole behavior. The results were consistent with a one-time stripping of about 10% of the material off a planet at least 14 times the mass of Jupiter, which then fell on the black hole and heated up.

In the scenario proposed in the new paper, the super-Jupiter drifted close to the supermassive black hole in NGC 4845. The gravitational attraction on the near side of the planet was stronger than on the far side, pulling it out of shape. (This is known as the tidal force, and it is responsible for the twice-daily tides on Earth.) At some point, the internal force of gravity holding the planet together was insufficient to keep the black hole from ripping about 10 percent of the mass off in one burst. [Read more...]

Black hole sez: I maded you a planet, but I eated it

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OK, I might be feeling a little cranky about this, but my article for Ars Technica is a little more measured. I’ll have a longer analysis for Galileo’s Pendulum tomorrow, for those who want it. The short version: the Alpha Magnetic Spectrometer (AMS-02) is a particle detector installed on the International Space Station. For several months, the lead investigator has been hinting that AMS-02 detected the signature of dark matter annihilation: collisions between dark matter particles producing an excess of positrons. However, the actual research paper was rather short on dark matter, however interesting the AMS-02 results really were.

The Alpha Magnetic Spectrometer (AMS-02) is a particle detector based on the International Space Station, designed for looking at a variety of particles from many sources, among them dark matter collisions. Recently, the AMS-02 research team announced the results of its first 18 months of data collection. These results are frustratingly ambiguous: while AMS-02 found an excess of certain type of particle expected from some models of dark matter annihilation, this excess didn’t bear the hallmarks predicted for a dark matter signature. So, something interesting is going on in the AMS-02 data, but the chances of dark matter being the cause seem a bit low. [Read more...]

Update: I published my rant over at Galileo’s Pendulum, explaining exactly why I’m grumpish about the way these results were announced and characterized in much of the media.

Much ado about nothing in today’s dark matter non-announcement

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White dwarf supernovas—more officially known as type Ia supernovas—are important to cosmologists because they all explode in very similar ways. That means they can be used to measure distances to faraway galaxies. However, a peculiar type of supernova, first identified in 2002, has a lot in common with type Ia explosions, but with a lot less energy. Some astronomers are now saying this could be a new class of white dwarf supernova that produces much less light and sends material into interstellar space at far lower speeds.

Beginning in 2002, astronomers started recognizing a peculiar type of explosion. Since then, they’ve identified 25 of them; they resemble white dwarf supernovas in many respects, but strongly differ in others. A new paper by Ryan J. Foley and colleagues offered an explanation: these were an entirely new type of white dwarf explosion, one involving less energy and more material from a companion star. So much less energy, in fact, that the authors suspect that the white dwarf may not be fully destroyed in these odd events. [Read more...]

Baby boom-ers could be a new type of white dwarf supernova

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Eta Carinae, one of the best candidates for going supernova in our lifetimes - assuming we understand the physics of the system, which we don't. [Credit: NASA, ESA, and the Hubble SM4 ERO Team]Supernovas are some of the most violent phenomena in the cosmos, but we’re in no immediate danger from one. However, astronomers would really really really like one to go off relatively nearby during our lifetimes, since we would learn a lot from observing one. My latest piece at Ars Technica is a gallery showing some of the more interesting supernova candidates in our galaxy, including a few that might possibly go kaboom while I’m still around to see it happen.

Supernovas and Marvin the Martian