The image above is of a star known as T Tauri. T Tauri is the prototype (primary example) of T Tauri type stars. In many ways T Tauri is a star in the making. Not quite a main sequence star, but more than a protostar.
Testing Metal
When it comes to planetary systems, it’s generally been thought that planets would tend to form around stars with a higher metallicity. At a broad level that makes sense because rocky planets such as Earth can only form in a system where there are enough metals like iron, silicon, carbon and the like. You can’t make a terrestrial planet out of just hydrogen and helium. But now that we’ve discovered lots of exoplanetary systems, we can actually put this idea to the test. A recent paper in Nature has done just that, and they’ve found something rather interesting.
Snapshot
Suppose an advanced alien race discovered our little planet. From their great telescopes they could tell our atmosphere is rich in oxygen and water vapor, which would indicate this was a planet inhabited by living organisms. They therefore decide to send a probe to study our curious blue world. With their advanced technology, this alien species can send a probe across the vast distance of space using a device they call the Maguffin drive. The Maguffin drive can transport the probe to Earth almost instantly, but because of the tremendous energy it requires the probe can only stay on Earth for one second.
Four of a Kind
One of the most popular constellations is Orion the hunter. In the sword of Orion, just below the belt is a nebula known as the Orion Nebula. This nebula is a stellar nursery about 1300 light years away. At the heart of the Orion Nebula is a small cluster of very bright stars known as the Trapezium Cluster. Because Trapezium is bright and reasonably close to us, we’re able to make very precise measurements of the stars’ speed and motion. What we find is a bit of a puzzle.
It’s a Gas
Stars form within large clouds of gas and dust known as stellar nurseries. Of course, when a star forms, that leaves less gas and dust to form other stars. So you can do a bit of simple math concerning star formation. Take the rate at which new stars form in a galaxy (and their typical mass), compare that to the amount of gas and dust a galaxy has, and you can estimate the time over which stars can form.
Twenty Percent Off
Contrary to popular belief, we haven’t directly observed most of the exoplanets we’ve discovered. The planets are too small and dim to be imaged directly. With the transit method, the amount the star dims determines the size of the planet relative to the star. For example, if we see a star dim by 1%, we know that the planet blocked 1% of the star, so we know the planet is 1% that of the star. To determine the size of the star, we typically look at the background flicker of starlight, which allows us to determine its size. Now a new paper in Astrophysical Journal Letters finds that we may have been underestimating the size of some stars, thus their planets may be larger than we’ve thought.
False Positive
Last year a paper in the Astrophysical Journal announced the discovery of two super-Earths orbiting a low metallicity Sun-like star known as HD41248. This was kind of a big deal, because it demonstrated that low metallicity stars could have rocky planets. Most of the known exoplanets are around higher metallicity stars. The two planets were discovered by observing the radial motion of the star (it motion toward or away from us) as measured by the Doppler shift of the starlight. Now a new paper in Astronomy and Astrophysics demonstrates that the planets likely don’t exist.
Second Look
One of the advantages of modern astronomy is that most observational data gets stored in a raw form. This is particularly true for the major space telescopes. Most of that raw data is also stored publicly, either a certain time period or even as the data is gathered. This means that long after an observation is made, people can go through the data to analyze it in new ways. As a case in point, a team recently gathered old data from the Hubble Space Telescope, and processed it using new methods.
Hydrogen, Helium, Metal
There’s an old joke that the astronomer’s periodic table consists of three elements: hydrogen, helium, and metal. It’s a nice joke, but when you understand how little of matter in the universe is “metal”, you can understand why astronomers focus on hydrogen and helium.