Hubble spots a ‘superbubble’ in a beautiful emission nebula

The Hubble Space Telescope may be experiencing problems this week, but it continues to offer a massive trove of data for astronomers to explore — including this week’s image of the beautiful and mysterious nebula N44.

This nebula has a highly unusual feature: A hole in its center, hundreds of light-years across, which forms a gap called a “superbubble.” N44 is a type of nebula called an emission nebula, which means it is a cloud of dust and gas which has been ionized by radiation from nearby stars and so which emits light in the visible wavelength. However, emission nebulae don’t typically have big holes in their centers, and scientists are still figuring out why N44 has this odd feature.

A dark, starry gap called a “superbubble,” visible in this Hubble Space Telescope image of Nebular N44 in the upper central region.
N44 is a complex nebula filled with glowing hydrogen gas, dark lanes of dust, massive stars, and many populations of stars of different ages. One of its most distinctive features, however, is the dark, starry gap called a “superbubble,” visible in this Hubble Space Telescope image in the upper central region. NASA, ESA, V. Ksoll and D. Gouliermis (Universität Heidelberg), et al.; Processing: Gladys Kober (NASA/Catholic University of America)

“The hole is about 250 light-years wide and its presence is still something of a mystery,” the Hubble scientists write. “Stellar winds expelled by massive stars in the bubble’s interior may have driven away the gas, but this is inconsistent with measured wind velocities in the bubble. Another possibility, since the nebula is filled with massive stars that would expire in titanic explosions, is that the expanding shells of old supernovae sculpted the cosmic cavern.”

N44 is huge, spanning 1,000 light-years across, and is located 170,000 light-years away in a satellite galaxy of the Milky Way called the Large Magellanic Cloud. Researchers have identified the bright blue area shown at the bottom right of the bubble as being the hottest region where stars are being formed at the fastest rate. The creation of hot stars gives rise to stellar winds which are unusually powerful in this nebula, reaching incredible speeds of over 4 million miles per hour.

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