The MESSENGER (MErcury Surface Space ENvironment, GEochemistry, and Ranging) spacecraft has found strong evidence both for water ice and organic molecules in shadowed craters near Mercury’s poles. Unlike Earth, Mercury has no seasons: its axis stands perpendicular to its plane of orbit, so deep craters near the north and south pole will have bottoms in permanent shade. Any place else on the surface will eventually be exposed to the Sun’s punishing glare, not only melting ice but boiling away any residual water. However, during the early Solar System, meteorites and comets brought water and organic compounds to the planet’s surface—at least according to planet formation models. This new discovery lends strong support to that theory.
The results from both the reflection and neutron analyses were consistent: several craters in Mercury’s polar regions provide sufficient shadow for stable water ice. The large craters named Prokofiev and Kandinsky were both found to contain significant radar-bright (RB) patches, indicating highly reflective materials. (Craters on Mercury are commonly named for famous artists, authors, composers, and the like. As a fan of both Prokofiev and Kandinsky, I approve.)
The size of the reflective patches matched the total proportion of each crater that lies in permanent shadow. [Read more...]
The observation of the freakishly huge black hole was made using the Hobby-Eberly Telescope (HET) at the McDonald Observatory in Texas. Since I had just visited the HET as part of the research for my book, I submitted one of my photos to illustrate the story…and it was accepted! [Credit: moi]
Most galaxies we know of have a supermassive black hole at their cores. These black holes may be millions or billions of times the mass of the Sun, but they are generally proportionate to the size of their host galaxies—or more properly, the central bulge of those galaxies. Up until recently, I wouldn’t have said “generally”, I would have said “always”. However, the compact galaxy NGC 1277 was recently found to have a hugely oversized black hole. Not only is this black hole huge in comparison to its host
, it’s one of the most massive yet found.
A new observation has revealed a galaxy that isn’t just bending the rule, but completely breaking it. In most systems, the black hole’s mass is about 0.1 percent of the mass of the galaxy’s central bulge. Remco van den Bosch and colleagues identified a black hole with a mass that’s about 59 percent of the mass of the central bulge. In fact, this black hole is one of the most massive ever observed, a striking discovery in a galaxy much smaller than our own. The galaxy itself is a bit on the small side, and the researchers suggest that we might want to look at the black holes in more galaxies this size. [Read more...]
I write articles and posts on a lot of different topics, both for my own blog and at Ars Technica. Many of those subjects drift pretty far from my putative area of expertise, but occasionally I get to write about something I know pretty well. To wit: last week, a group of researchers using the 4-meter Blanco telescope at Cerro Tololo (best known for its use in discovering dark energy in 1998) have measured distances to galaxy clusters very precisely. (Here’s my galaxy cluster primer, written as a podcast for 365 Days of Astronomy.) Their study, as with a major chunk of my thesis work, was intended to pin down the effect of dark energy—cosmic acceleration—on galaxy cluster formation and evolution. In particular, if dark energy’s effects change over time, that would have a profound influence on the number and size of galaxy clusters that form in a given era. To get a handle on this, we need a detailed census of clusters, dating back to the earliest times.
A new survey of galaxy clusters marks the beginning of a promising effort to map the birth and growth of galaxy clusters back to relatively early times. Jeeseon Song and colleagues used optical and infrared telescopes to measure the distances of 158 bright clusters in a large patch of the southern sky, looking back in time to when the Universe was less than one-third its current age. These observations provide the beginnings of a history of galaxy cluster evolution, which should help constrain models of dark energy. [Read more...]
The dwarf planet Makemake (pronounced MAHkayMAHkay) is about 2/3 the diameter of Pluto, and farther from the Sun. That makes it hard to observe. Astronomers using a set of telescopes in South America tracked it during an occultation: a brief interval when it passed in front of a faint star. By measuring the light curve—the variation in light as Makemake eclipsed the star—the researchers determined that the dwarf planet has no substantial atmosphere, and probably no sizable moon.
Makemake potentially occults three stars in a typical year, though not all of these are useful, due to the faintness of the background star. The current study involved an occultation visible from South America on April 23, 2011. Just as eclipses may be partial or total, the “shadow” of Makemake passed over a swath of the continent, allowing telescopes in various locations to measure the passage of the star behind different parts of the dwarf planet. The researchers tried to obtain data from 16 telescopes, but only 7 of those returned successful measurements.
Each telescope saw a clear, sharp drop in the background star’s light, a strong indicator that Makemake has no substantial atmosphere. [Read more....]
Macroscopic processes are usually not completely reversible: you can’t unmix or unbake cake, and perfume released from a bottle won’t spontaneously recollect. However, these phenomena involve huge numbers of particles. On the level of individual particles in elementary physics, the direction of time doesn’t matter to the forces involved. The exception to this is the weak force, one of the four fundamental forces of nature. However, no experiment thus far had been able to demonstrate time asymmetry unambiguously until now.
New results from the BaBar detector at the Stanford Linear Accelerator Center (SLAC) have uncovered this asymmetry in time. Researchers measured transformations of entangled pairs of particles, including the rates at which these transformations occurred. Through analyzing over 10 years of data, they found clear time-reversal asymmetry with an error of only one part in 1043, a clear discovery by any standard. These results are a strong confirmation of predictions of the Standard Model, filling in one of the final missing details of that theory. [Read more...]
Successful techniques exist for bringing atoms down to really cold temperatures, into the regimes where the most exotic collective quantum phenomena appear. However, those same techniques don’t work for polyatomic molecules—those consisting of three or more atoms. This is a bit frustrating for physicists, since molecules have the potential to exhibit some truly wild quantum effects: parity violation (processes that depend on which direction they occur), quantum chemical effects, and—hopefully—new phenomena which we don’t expect. A new experiment has succeeded in using three different types of light in tandem to bully molecules down to cold temperatures, a process known as Sisyphus cooling.
For this reason, the researchers in the present study turned to a more elaborate technique, where multiple processes were utilized in succession to cool the molecules. The experimenters sent a stream of molecules into a trap made from standing microwaves crossed with an infrared laser beam. The trap itself consisted of a sort of radio antenna; by varying the frequency of the radio waves, the researchers could extract energy from the molecules rapidly.
The combination of the excitation with a laser and the jostling by radio waves boosted the energy state of the molecules slightly, but they lost even more energy when coming down, resulting in ever colder temperatures. This virtual harassment to produce ultracold temperatures gives the process its name of Sisyphus cooling, referring to the Greek myth of a wicked king punished in Hades to repeat a single task forever. [Read more....]
Many star systems seem to resemble our own Solar System: the planets orbit their host star in the same direction that the star spins. Admittedly, the data is still sparse: it’s not always possible to get that measurement. The brief version: you need the planet to transit or briefly eclipse its host star, and you need to be able to measure the small change in the star’s spectrum. This is most easily done when the planet is close in and relatively large—a class of exoplanets known as hot Jupiters, since they are big and close enough to experience extreme temperatures. Surprisingly, some of these hot Jupiters orbit their stars the wrong way, and this misalignment is difficult to explain within the standard theory of planet formation. However, a new model suggests that if the original star system had two stars, it would mess up the protoplanetary disk, leaving orbits askew.
In this revised model, strongly misaligned orbits are the result of another factor that influenced planet formation: a second star in the system. The gravitational influence of the companion star twisted the orbit of the exoplanet, pulling it out of alignment. And, in many cases, the star would leave little trace beyond the altered orbits: Sun-like stars often form in pairs or larger assemblies, but some of them evaporate over time. [Read more....]