Protostars are, as the name suggests, what we have before a star forms. Clouds of gas and dust collapse under gravitation, heat up, and (at least in some cases) begin fusing hydrogen into helium in their cores. A new observation of a protostar catches it very early in its formation, while it was still accreting mass. The researchers estimated it might have been 300,000 years old or even less, which may sound like a lot, but is a blink of an eye in cosmic terms.
The researchers measured dust in the region surrounding L1527 using the Submillimeter Array (SMA) in Hawaii and the Combined Array for Research in Millimeter-wave Astronomy (CARMA) in California. Previous observations, using one of the Gemini telescopes in Chile, determined the protostar had a disk, which appears edge-on from our perspective on Earth.
The newer results determined both the thermal emission—the broad spectrum of light directly emitted from the warm gas and dust—and absorption by carbon monoxide molecules in the disk. (Specifically, they measured 13CO, the version of carbon monoxide involving the isotope carbon-13.) The excellent resolution of the telescopes enabled the astronomers to measure the total size and mass of each component of the system. [Read more…]
Map of the Moon’s surface, as provided by the twin GRAIL spacecraft.
For most astrophysics purposes, we don’t have to worry about the details of the inner structure of planets and moons. However, if we want to reconstruct their full history, it helps to know all the variations in density and composition. The twin GRAIL spacecraft in orbit around the Moon are designed to do just that. By a bit of fancy formation flying, GRAIL-A (“Ebb”) and GRAIL-B (“Flow”) have provided the most detailed map yet of the Moon’s surface and interior, by measuring fluctuations in the gravitational pull. My editor John Timmer and I wrote a pair of stories (not named Ebb and Flow) describing the spacecraft and their discoveries. The Moon turns out to have had an even more violent past than previously suspected, including an impact so powerful it shattered the crust.
Each GRAIL spaceship is about 200kg in mass and the size of a refrigerator. The craft follow a nearly polar orbit, looping around the Moon such that, as it rotates on its axis, GRAIL was able to take measurements of the entire body in swaths (akin to the segments of an orange). [Read more…]
The moments after the Big Bang left the Universe very hot and dense. In that violent environment, the first nuclei came to be: hydrogen, helium, and lithium…but nothing heavier. The elements more massive than helium (which astronomers perversely refer to as “metals”) were forged by stars and spread through the Universe as those stars died. That means if we look far enough back in time, we should be able to see the era of transition: when the first metals in the Universe came to be. A new observation of the environment surrounding a quasar shining a mere 772 million years after the Big Bang has revealed a metal-free cosmos.
Modern galaxies like the Milky Way contain populations of stars that we can divide based on their metal content. The Sun is a Population I star, with a relatively high metal abundance; older, Population II stars near the galactic center are metal-poor. However, the earliest, metal-free stars—known as Population III—are still hypothetical. According to widely accepted models, Population III stars were massive and therefore short-lived, going supernova and spreading the first metals into interstellar space.
When did these first stars form, and did they actually correspond to our models? These questions are still unanswered. The crucial period of time when the first stars must have formed is still marked by a paucity of data. [Read more…]