Hot and Heavy Star Birth: Young cosmos delivers massive stars

Aided by a gravitational zoom lens, astronomers have discovered the hottest, brightest, and most crowded star-forming region observed so far. Ablaze with a million newborn stars, the Lynx arc, named after the constellation in which it resides, lies 12 billion light-years from Earth. Telescope images of the Lynx arc thus reveal what conditions were like when the now 14-billion-year-old universe was only 2 billion years old. At that time, only a few generations of stars had lit up the cosmos.

Red-glowing gas (arrow) indicates the distant Lynx arc, the hottest and brightest star-forming region known. This composite view consists of an image taken in red light by the Hubble Space Telescope and six ground-based images recorded at visible-light and near-infrared wavelengths. Fosbury, et al., ESA/NASA/NOAO
STAR-BIRTH BOOM. Artist’s depiction of the massive young stars burning brightly in the Lynx arc, as it would appear if the star-birth region were in our own galaxy rather than 12 billion light-years away. Fosbury, et al., ESA/ NASA

With a surface temperature of some 80,000C, the Lynx stars blaze twice as hot as the brightest star in our galaxy’s Orion star-forming region does. That heat and the stars’ white-blue color suggest that all these newborns are about 10 to 20 times more massive than the sun. In comparison, the Orion region has only four such massive stars.

The stellar masses in the Lynx arc are intriguing to astronomers because computer simulations have indicated that the first stars to have formed in the universe were even more massive, several hundred times as heavy as the sun (SN: 6/8/02, p. 362: Cosmic Dawn).

The Lynx arc stars might represent transitional objects, less massive than the first-generation stars but weightier than the average star born today, says Robert A.E. Fosbury of the European Space Agency in Garching, Germany. He and his colleagues describe their findings in the Oct. 20 Astrophysical Journal.

The Lynx arc “is the closest we have come so far” to seeing primordial star-forming regions, says Fosbury.

Although the Lynx arc is bright, its great distance from Earth would ordinarily have rendered it too faint to be detected. But a massive cluster of galaxies happens to lie along the line of sight between Earth and the Lynx arc. The gravity of the cluster acts as a lens, bending and magnifying the light from the Lynx arc by a factor of 10.

Ionizing radiation from the Lynx stars blasts surrounding gas. Fosbury and his colleagues analyzed spectra of the energized gas to discover the color, temperature, and therefore weighty nature of the stars.

The chance alignment of the Lynx arc, the galaxy cluster, and Earth “is offering us insight into what the next-generation telescopes are going to provide routinely, namely, glimpses of some of the first star-forming places in the universe,” says Stephen E. Strom of the National Optical Astronomy Observatories in Tucson.


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