“Fossil” galaxy, Segue 1, is a satellite of the Milky Way and, with just a few hundred stars, it’s so tiny that it’s not clear whether it’s actually a galaxy or just a globular cluster (a tightly-packed grouping of old stars that orbits in the halo of our galaxy). What makes Segue 1 interesting is that, unlike other galaxies, it appears to have stopped changing with time almost immediately after it formed. Galaxies go through periods of intense activity throughout their lifetimes — e.g. bursts of star formation — but not so with Segue 1.

Elements heavier than helium are almost entirely produced inside the cores of stars or during supernovae, and are expelled back into space via red giant winds or supernova explosions, where these elements mix with what’s called the interstellar medium (mostly hydrogen and helium). The next generation of stars forms out of this mixed gas, therefore we expect to find heavier elements in the atmospheres of younger stars, and that’s what astronomers indeed observe. The stars in Segue 1, however, are pristine and comprised almost entirely of hydrogen and helium — its stars contain 300 times less heavy elements than our Sun. It appears that star formation in this tiny galaxy shut off almost as soon as it began. Astronomers refer to it as a “fossil” galaxy, because it’s been preserved just as it was nearly 13 billion years ago, and as such it should give some important insights into the conditions of the early universe.

The evidence for dark matter mounts: gamma rays (very high energy particles) observed coming from dwarf galaxies suggest the annihilation of dark matter particles that collide with each other. The problem: calculations show that these particles would have to be heavier than previously believed, which is at odds with hints from earthly experiments designed to detect the mysterious particles.

One of Saturn’s moons, Enceladus, appears to have a liquid ocean beneath its frozen crust. Scientists are searching for liquid water on solar system bodies other than the Earth, because life as we know it can’t exist without liquid water.

NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) probe is expected to crash into the Moon on April 21. The probe, which has been in orbit around the Moon since October of last year, has been gathering data on the Moon’s extremely thin atmosphere (I bet you didn’t know the Moon has an atmosphere—so does Mercury). Very soon, LADEE will run out of fuel and its orbit will decay, sending it crashing onto the surface of the Moon.

The big, fat ‘El Gordo’ galaxy cluster is bigger than previously thought. New Hubble Space Telescope data, showing how much the giant cluster is warping the space around it, has allowed a more precise calculation of its mass, which now appears to be three million billion times the mass of the Sun (3 x 10¹⁵ solar masses). What makes El Gordo so interesting is not necessarily its large mass—there are other massive clusters in the universe—but that it got so massive so early in the history of the universe. Like all galaxy clusters, the majority if its mass is comprised of dark matter, not the visible stuff you can see.