M60-UCD1 in 60 Seconds

Narrator (April Hobart, CXC): Astronomers may have discovered the densest galaxy in the nearby Universe. The galaxy, known as M60-UCD1, is located about 54 million light years from Earth. M60-UCD1 is packed with an extraordinary number of stars and this has led scientists to classify it as an "ultra-compact dwarf galaxy." This means that this galaxy is smaller and has more stars than just a regular dwarf galaxy. While astronomers already knew this, it wasn't until these latest results from Chandra, Hubble and telescopes on the ground that they knew just how dense this galaxy truly is. M60-UCD1 has the mass about 200 million times our Sun and, remarkably, about half of this mass is packed into a radius of just about 80 light years. That translates into the density of stars in this part of M60-UCD1 being about 15,000 times greater than what's found in Earth's neighborhood in the Milky Way. Astronomers have been trying to determine where these ultra-compact dwarf galaxies fit into the galactic evolutionary chain. Some have suggested they start off not as galaxies but as giant star clusters. The latest results on M60-UCD1 challenge that idea. The new Chandra data indicate that there may be a supermassive black hole at the center of M60-UCD1. If that's the case, then it's unlikely this object could have ever been a star cluster. Instead, the X-ray data point to this galaxy being the remnants of a larger galaxy that had its outer stars ripped away by tidal forces, leaving behind the dense inner core of the galaxy. Other information about M60-UCD1 including its large mass, point to the same conclusion. Regardless, this galaxy is a fascinating object that astronomers will be studying for a long time to come.

Return to Podcasts

HD 189733: NASA's Chandra Sees Eclipsing Planet in X-rays for First Time

View/Listen
Narrator (April Hobart, CXC): HD 189733b: An exoplanet in orbit around a star about 63 light years from Earth. It has been nearly two decades since the first exoplanets – that is, planets around stars other than our Sun – were discovered. Now for the first time, X-ray observations have detected an exoplanet passing in front of its parent star. The observations, made by NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton Observatory, took advantage of the alignment of a planet and its parent star in HD 189733. This alignment enabled the observatories to observe a dip in X-ray intensity as the planet moved in front of, or transited, the star. This technique is the one used so successfully at optical wavelengths by NASA's Kepler telescope. In earlier studies using optical light, astronomers discovered that the main star in the HD 189733 system had what is known as a "hot Jupiter" around it. This means the planet is about the size of Jupiter, but in very close orbit around its star. The planet – that has been named HD 189733b -- is over 30 times closer to its star than Earth is to the Sun, and goes around the star once every 2.2 days. The new X-ray data suggest that this planet has a larger atmosphere than previously thought. This, in turn, may imply that radiation from the parent star is evaporating the atmosphere of HD 189733b more quickly than expected. The results on HD 189733 demonstrate how we need information from many different telescopes that detect different types of light to get a fuller picture of these mysterious worlds that we are now able to explore.

PODCASTS | MAIN MENU