Podcast: The Impending Intergalactic Cloud Collision

Not too far away, there’s a giant gas cloud drifting towards the Milky Way galaxy. Known as the Smith Cloud and made up mostly of hydrogen, it should merge with our home system in about 30 million years. On this week’s podcast, I spoke with Jay Lockman, the lead scientist at the NRAO’s Green Bank Telescope in West Virginia who told me about this mysterious object.

A false-color image of the Smith Cloud, showing it’s comet-like appearance.

As big as a small galaxy, scientists think that when the Smith Cloud merges with the Milky Way, it will trigger a whole new era of star formation in our own galaxy. A collision with a massive gas cloud might seem ominous, but astronomers say not to worry. Collisions like this probably have already happened even closer to us that where the Smith Cloud is going to hit, and planet Earth is still going strong.

The Smith Cloud on a collision course with the Milky Way galaxy.

However scientists have been confused as to how the cloud has been able to hold itself together at all. According to simulations, the hot gas and dust surrounding the Milky Way should have ripped the cloud apart eons ago. But recent studies indicate that the gas scientists have been observing might just be the tip of the iceberg of what’s out there. They think that the cloud is just a small patch of normal matter bound together at the heart of an even bigger dark matter cloud.

This as yet unpublished image from the Green Bank Telescope shows how it sees the cloud’s
radio emissions in hydrogen’s 21 cm emission band.
Image: Jay Lockman

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