脆弱的超大星系是宇宙史中缺失的一环

Two hungry young galaxies¹ that collided 11 billion years ago are rapidly forming a massive galaxy² about 10 times the size of the Milky³ Way, according to UC Irvine-led research published Wednesday in the journal Nature. Capturing the creation of this type of large, short-lived star body is extremely rare -- the equivalent of discovering a missing link between winged dinosaurs⁴ and early birds, said the scientists, who relied on the once-powerful Herschel space telescope and observatories⁵ around the world. The new mega-galaxy, dubbed⁶ HXMM01, "is the brightest, most luminous⁷（明亮的） and most gas-rich submillimeter-bright galaxy merger⁸ known," the authors write.

 

HXMM01 is fading away as fast as it forms, a victim of its own cataclysmic（大变动的） birth. As the two parent galaxies smashed together, they gobbled up huge amounts of hydrogen, emptying that corner of the universe of the star-making gas.

 

"These galaxies entered a feeding frenzy⁹ that would quickly exhaust the food supply in the following hundreds of million years and lead to the new galaxy's slow starvation for the rest of its life," said lead author Hai Fu, a UC Irvine postdoctoral scholar.

 

The discovery solves a riddle¹⁰ in understanding how giant elliptical（椭圆的） galaxies developed quickly in the early universe and why they stopped producing stars soon after. Other astronomers¹¹ have theorized that giant black holes in the heart of the galaxies blew strong winds that expelled the gas. But cosmologist Asantha Cooray, the UC Irvine team's leader, said that they and colleagues across the globe found definitive¹² proof that cosmic mergers¹³ and the resulting highly efficient consumption of gas for stars are causing the quick burnout.

 

"Finding this type of galaxy is as important as the discovery of the archaeopteryx was in understanding dinosaurs' evolution into birds, because they were both caught at a critical transitional phase," Fu said.

 

The new galaxy was initially¹⁴ spotted¹⁵ by UC Irvine postdoctoral scholar Julie Wardlow, also with Cooray's group. She noticed "an amazing, bright blob" in images of the so-called cold cosmos¹⁶ -- areas where gas and dust come together to form stars -- recorded by the European Space Agency's Herschel telescope with important contributions from NASA's Jet Propulsion Laboratory in Pasadena. "Herschel captured carpets of galaxies, and this one really stood out."

 

Follow-up views at a variety of wavelengths¹⁷ were obtained at more than a dozen ground-based observatories, particularly the W. M. Keck Observatory¹⁸ in Hawaii.

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