Traversing Space on a Bridge of Stars

A Bridge of Stars between the Magellanic Clouds

The Magellanic Clouds.

The Magellanic Clouds in the night sky. The Large and the Small Magellanic Clouds are visible. The Clouds are moving towards the bottom left corner. Credit: V. Belokurov and A. Mellinger

If you’ve ever been south of the equator, you’ve probably seen the Magellanic Clouds in the southern hemisphere sky. These two little galaxies  look like puffy clouds separated by a whole lot of space. It turns out that the light-years between them might not be so empty as astronomers once thought. Researchers at University of Cambridge in England have found what looks like a 43,000 light-year-long bridge of stars stretching from one galaxy to the other.  Their work, based on a huge census of stars that the Gaia satellite is doing, is giving a new look at what happens when dwarf galaxies interact. The result of its mission, when completed, will be a 3D map of our galaxy, and apparently of our neighboring satellite galaxies.

Using Old Stars to Trace a Bridge

bridge of stars

The Magellanic Clouds, their stellar halos and the RR Lyrae bridge. Pale white veils and the narrow bridge pf stars between the Clouds represent the distribtuion of the RR Lyrae stars detected with the data from the Gaia satellite. Credit: V. Belokurov, D. Erkal and A. Mellinger

The team of astronomers focused their attention on data about stars called RR Lyraes. These are pulsating variables that are quite old stars. They’ve been around for a long time — at least as long as the Magellanic Clouds have existed. So, their very existence tells us something about the history of these two nearby dwarf satellite galaxies. Theastronomers used the RR Lyraes to measure the extent of the Large Magellanic Cloud first. It turns out there’s a sort of fuzzy halo of these stars stretching away from the LMC that’s being stretched out into a evanescent bridge of stars.

The big question now is why this stream exists. Normally streams of stars aren’t stretching away from a galaxy unless there’s been something to tear them away. In this case, it’s likely that the tidal pull of the e Small Magellanic Cloud has steadily lured away stars from the LMC.  As it orbits, the LMC is leaving a tracer of its stars as it goes.  There could also be stars in the stream that are being attracted by the gravity of the Milky Way, too.

A Bridge of Stars During Interactions

Interactions between galaxies often warp and reshape the participants in the galactic dances. Such interactions are also an integral part of the galaxy assembly process: big galaxies get built from the collisions of smaller ones. We’ve seen streams of stars in other interacting galaxies, so this lovely bridge between the Magellanic Clouds fits right into the idea that cosmic dances can do more than warp galaxies. They can strip stars away, too.

This is a pretty cool story of galaxy evolution taking place in our own galactic back yard. If you want more information on the work the Cambridge astronomers are doing, check out their press release here.




Spotting Planets Around Other Stars

Clockwork Worlds: Recording Planets and their Orbits from a Distance

Wow, this is really cool. Watch this little video a few times…it’s a time-lapse sequence of planets orbiting a star about 129 light-years away from us in the direction of the constellation Pegasus. The time-lapse was made over a period of years starting in 2009. These planets — which are Jupiter-size and larger — lie quite far from their star; their orbits range from 40-year periods for the closest one to 400 years for the most distant one. You can read more about their discovery and the work astronomers have done to chart their orbits at NASA Astrobiology

Not so long ago, worlds like these were lost in the glare of their stars, and it fell to astronomers to devise ways to block out the starlight so they could even have a chance of spotting distant planets. Now, using such instruments as the Gemini Planet Imager, they can do that.

I find it remarkable that we can “see” these planets. Finding alien worlds is more than just a science-fiction adventure. It’s key to understanding many things about our own solar system and about the environment of our galaxy. Sure they look like dots of light, but they’re worlds. Maybe not just like our own, but they’re still distant worlds, and gives us yet more proof that our galaxy is a veritable treasure trove of exoplanets. It now appears that the galaxy is rich with them, as the Kepler mission showed us so dramatically when it surveyed just a tiny portion of the galaxy. I really think that more discoveries await. The next steps will be to study the planets we find in great detail to learn more about their atmospheres as well as their progression as they are born and evolve in their systems. All of this leads inexorably to looking for life.   That will be a huge challenge, but given how far we’ve come now in our planet searches, I’m sure that astronomers and astrobiologists will figure it out, perhaps within our lifetimes. Stay tuned!