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…]
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).
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.)
The New Yorker recently started “Elements”, a science and technology blog. Their most recent contributor is…me! I covered a strange little controversy begun when the International Astronomical Union (IAU), a professional society with over 10 thousand members, decided to pick a fight with a company offering a contest to name exoplanets. That company, Uwingu, decided to fight back, and the exchange highlighted a set of philosophical questions about who gets to name new worlds.
However, the International Astronomical Union, a society of professional astronomers, strongly disapproves of the entire concept, and published a statement to that effect (though without mentioning Uwingu by name). According to its Web site, the I.A.U.’s tasks include serving “as the internationally recognized authority for assigning designations to celestial bodies and surface features on them.” The process of naming new objects is complicated (the Web précis of the document is itself formidable), and the I.A.U. press release claims exclusive rights to decide what a planet is called—even over the wishes of the scientist or scientists who discovered it. [Read more…]
Now, can I get a picture of Eustace Tilley wearing a bowler hat?
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…]
In a certain sense, it’s easy to keep things in orbit around Earth. However, it’s hard to keep satellites in a specific orbit, which is what matters most for communicating with them and they with us, whatever task they’re designed to perform. Thanks to the work of rocket engineer Yvonne Brill in the early 1970s, the process is remarkably automatic.
Brill’s design eliminated this redundancy and lightened the spacecraft in the process. She also used a type of fuel called hydrazine, which is so reactive you don’t need oxygen or another chemical injection to ignite it. (On Earth, we’ve got lots of oxygen available for making things burn, but in space, you need to carry your own fuel for fire.) Brill’s system pumped liquid hydrazine through an aluminum nozzle. The chemical composition of the nozzle reacted with it, splitting it into smaller molecules and releasing a lot of energy. [Read more…]
I’m no rocket scientist, but I can appreciate the challenges of engineering something that needs to stay in the same orbit for years or decades. Yet the New York Times obituary for Brill mentioned her remarkable achievements as a sort of afterthought, as though they weren’t very important, really, in the scheme of things. My piece isn’t an obituary—I mostly write explanatory pieces about science, after all—but Brill’s contribution to spaceflight in general and the communications satellite revolution of the 1980s is astounding.
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.
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…]
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.