HubbleSite.org | STScI-2010-38 | 18 Nov 2010
Hollywood-like Galactic Encounter Results in Baby StarsThese images, taken with NASA's Hubble Space Telescope, reveal fresh star birth in the ancient elliptical galaxy NGC 4150, located about 44 million light-years away. The images combine observations taken in visible and near-ultraviolet light with Hubble's Wide Field Camera 3. Ultraviolet light traces the glow of young stars.
In the large-scale image, NGC 4150 looks very much like a typical elliptical galaxy. The dark strands of dust in the center, however, provide tentative evidence of a recent galaxy merger. The inset image shows a magnified view of the chaotic activity inside the galaxy's core. Those regions within about 650 light-years of the center that are not obscured by dust appear bright in near-ultraviolet light (shown here in blue). The blue areas indicate a flurry of recent star birth. The stellar breeding ground is about 1,300 light-years across. The stars in this area are less than a billion years old. By comparison, most of the stars in the galaxy are about 10 billion years old. These young stars most likely formed during an encounter with a smaller galaxy that was about one-twentieth the mass of NGC 4150.
Elliptical galaxies were once thought to be aging star cities whose star-making heyday was billions of years ago. But new observations with NASA's Hubble Space Telescope are helping to show that elliptical galaxies still have some youthful vigor left, thanks to encounters with smaller galaxies.
Images of the core of NGC 4150, taken in near-ultraviolet light with the sharp-eyed Wide Field Camera 3 (WFC3), reveal streamers of dust and gas and clumps of young, blue stars that are significantly less than a billion years old. Evidence shows that the star birth was sparked by a merger with a dwarf galaxy. The new study helps bolster the emerging view that most elliptical galaxies have young stars, bringing new life to old galaxies. In the large-scale image, the dark strands of dust in the center provide tentative evidence of a recent galaxy merger. The inset image shows a magnified view of the chaotic activity inside the galaxy's core. The blue areas indicate a flurry of recent star birth. The stellar breeding ground is about 1,300 light-years across. The stars in this area are less than a billion years old.
Universe Today | Nancy Atkinson | 18 Nov 2010
Anatomy of a post-starburst minor merger: a multi-wavelengthWFC3 study of NGC 4150 - RM Crockett et alLike news ripped from a Hollywood tabloid, this saga includes an encounter between two individuals; one aging, and thought to be past its prime, the other youthful and vigorous. And for good measure, thrown in on this story are cannibalism and even zombies. The result of the meet-up? Babies. Baby stars, that is, and the individual galaxies in this tale are about as opposite as they could be. Yet their encounter ended up as happily- ever-after. The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) captured images of NGC 4150, an aging elliptical galaxy, and at the core of the galaxy was some vigorous star birth. The star-making days of this galaxy should have ended long ago, but here was active star birth taking place. This isn’t the first time astronomers have seen something like this, so they took a closer look.
Near-ultraviolet images of this old elliptical galaxy taken by WFC3 revealed streamers of dust and gas and clumps of young, blue stars, significantly less than a billion years old. But also there was evidence of an encounter — dark strands of dust in the center provided tentative evidence of a recent galaxy merger.
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And so, a new study by Crockett and his team helps bolster the emerging view that most elliptical galaxies have young stars, bringing an old, dying galaxy back to life. The inset on the top image shows a magnified view of the chaotic activity inside the galaxy’s core. The blue areas indicate a flurry of recent star birth. The stellar breeding ground is about 1,300 light-years across.
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Crockett and his team selected NGC 4150 for their Hubble study because a ground-based spectroscopic analysis gave hints that the galaxy’s core was not a quiet place. The ground-based survey, called the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON), revealed the presence of young stars and dynamic activity that was out of sync with the galaxy.
- Accepted for publication in The Astronomical Journal (pdf)
He is fast when it comes to Hubble news breaks. 
