Holmberg II – Forever Blowing Bubbles

Hubble’s famous images of galaxies typically show elegant spirals or soft-edged ellipses. But these neat forms are only representative of large galaxies. Smaller galaxies like the dwarf irregular galaxy Holmberg II come in many shapes and types that are harder to classify. This galaxy’s indistinct shape is punctuated by huge glowing bubbles of gas, captured in this image from the NASA/ESA Hubble Space Telescope.


“I’m forever blowing bubbles… Pretty bubbles in the air…” Its name is Holmberg II, and it’s a dwarf galaxy that’s only 9.8 million light-years away. It’s part of the M81 Galaxy Group and one of the few that isn’t distracted by gravity from nearby peers. Holmberg II is an active little galaxy and one that’s full of holes – the largest of which spans 5500 light years wide. But what makes this one really fascinating is that it’s expelling huge bubbles of gas…

Here the remnants of mature and dying stars have left thick waves of dust and gas, carved into shape by stellar winds. Some ended their lives as supernovae – sending rippling shockwaves through the thinner material to hang in space like fantasy ribbons. With no dense nucleus to deform it like an elliptical galaxy, nor distorting arms like a spiral, this irregular star-forming factory is the perfect place for astronomers to take a close look stellar formation in a new way.

Keep thinking bubbles, because Holmberg II is the perfect example of the “champagne” model of starbirth – where new stars create even newer ones. How does it work? When a bubble is created by stellar winds, it moves outwards until it reaches the edge of the molecular cloud that spawned it. At the exterior edge, dust and gas have been compressed and form a nodule similar to a blister. Here another new star forms.. and triggers again… and triggers again… similar to the chain reaction which happens when you open a bottle of champagne.

And fill the glass again, because Holmberg II is also known as Arp 268. While Halton Arp certainly knows his stuff when it comes to unusual galaxies, there’s even more. According to the Hubble team, our little dwarf also has an ultraluminous X-ray source in the middle of three gas bubbles which appears in the image’s upper right hand corner. No one is quite sure of what it just might be! Maybe black hole bubbles?

“They fly so high… Nearly reach the sky. Then in my dreams they fade and die…” Perhaps Dean Martin?

Original Story Source: Hubble News.