Early Stars Were Whirling Dervishes

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Even though some of the first stars in the early universe were massive, they probably lived fast and furious lives, as they likely rotated much faster than their present-day counterparts. A new study on stellar evolution looked at a 12-billion-year-old star cluster and found high levels of metal in the stars – a chemical signature that suggests that the first stars were fast spinners.

“We think that the first generations of massive stars were very fast rotators – that’s why we called them spinstars,” said Cristina Chiappini of the Astrophysical Institute Potsdam in Germany, who led the team of astronomers.

These first generation stars died out long ago, and our telescopes can’t look back in time far enough to actually see them, but astronomers can get a glimpse of what they were like by looking at the chemical makeup of later stars. The first stars’ chemical imprints are like fossil records that can be found in the oldest stars we can study.

The general understanding of the early universe is that soon after the Big Bang, the Universe was made of essentially just hydrogen and helium. The chemical enrichment of the Universe with other elements had to wait around 300 million years until the fireworks started with the death of the first generations of massive stars, putting new chemical elements into the primordial gas, which later were incorporated in the next generations of stars.

Using data from ESO’s Very Large Telescope (VLT), the astronomers reanalyzed spectra of a group of very old stars in the Galactic Bulge. These stars are so old that only very massive, short-living stars with masses larger than around ten times the mass of our Sun should have had time to die and to pollute the gas from which these fossil records then formed. As expected, the chemical composition of the observed stars showed elements typical for enrichment by massive stars. However, the new analysis unexpectedly also revealed elements usually thought to be produced only by stars of smaller masses. Fast-rotating massive stars on the other hand would succeed in manufacturing these elements themselves.

“Alternative scenarios cannot yet be discarded – but – we show that if the first generations of massive stars were spinstars, this would offer a very elegant explanation to this puzzle!” said Chiappini.

A star that spins more rapidly can live longer and suffer different fates than slow-spinning ones. Fast rotation also affects other properties of a star, such as its colour, and its luminosity. Spinstars would therefore also have strongly influenced the properties and appearance of the first galaxies which were formed in the Universe. The existence of spinstars is now also supported by recent hydrodynamic simulations of the formation of the first stars of the universe by an independent research group.

Chiappini and her team are currently working on extending the stellar simulations in order to further test their findings. Their work is published in a Nature article on April 28, 2011.

Source: University of Potsdam, Nature

VLT, Hubble Smash Record for Eyeing Most Distant Galaxy

Planck Time

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Using the Hubble Space Telescope and the Very Large Telescope (VLT), astronomers have looked back to find the most distant galaxy so far. “We are observing a galaxy that existed essentially when the Universe was only about 600 million years old, and we are looking at this galaxy – and the Universe – 13.1 billion years ago,” said Dr. Matt Lehnert from the Observatoire de Paris, who is the lead author of a new paper in Nature. “Conditions were quite different back then. The basic picture in which this discovery is embedded is that this is the epoch in which the Universe went from largely neutral to basically ionized.”

Lehnert and an international team used the VLT to make follow-up observations of the galaxy — called UDFy-38135539 – which Hubble observations in 2009 had revealed. The astronomers analyzed the very faint glow of the galaxy to measure its distance — and age. This is the first confirmed observations of a galaxy whose light is emerging from the reionization of the Universe.

The reionization period is about the farthest back in time that astronomers can observe. The Big Bang, 13.7 billion years ago, created a hot, murky universe. Some 400,000 years later, temperatures cooled, electrons and protons joined to form neutral hydrogen, and the murk cleared. Some time before 1 billion years after the Big Bang, neutral hydrogen began to form stars in the first galaxies, which radiated energy and changed the hydrogen back to being ionized. Although not the thick plasma soup of the earlier period just after the Big Bang, this galaxy formation started the reionization epoch, clearing the opaque hydrogen fog that filled the cosmos at this early time.

A simulation of galaxies during the era of deionization in the early Universe. Credit: M. Alvarez, R. Kaehler, and T. Abel

“The whole history of the Universe is from the reionization,” Lehnert said during an online press briefing. “The dark matter that pervades the Universe began to drag the gas along and formed the first galaxies. When the galaxies began to form, it reionized the Universe.”

UDFy-38135539 is about 100 million light-years farther than the previous most distant object, a gamma-ray burst.

Studying these first galaxies is extremely difficult, Lehnert said, as the dim light falls mostly in the infrared part of the spectrum because its wavelength has been stretched by the expansion of the Universe — an effect known as redshift. During the time of less than a billion years after the Big Bang, the hydrogen fog that pervaded the Universe absorbed the fierce ultraviolet light from young galaxies.

The new Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope discovered several candidate objects in 2009, and with 16 hours of observations using the VLT, the team was able to was used to detect the very faint glow from hydrogen at a redshift of 8.6.

The team used the SINFONI infrared spectroscopic instrument on the VLT and a very long exposure time.

“Measuring the redshift of the most distant galaxy so far is very exciting in itself,” said co-author Nicole Nesvadba (Institut d’Astrophysique Spatiale), “but the astrophysical implications of this detection are even more important. This is the first time we know for sure that we are looking at one of the galaxies that cleared out the fog which had filled the very early Universe.”

One of the surprising things about this discovery is that the glow from UDFy-38135539 seems not to be strong enough on its own to clear out the hydrogen fog. “There must be other galaxies, probably fainter and less massive nearby companions of UDFy-38135539,” said co-author Mark Swinbank from Durham University, “which also helped make the space around the galaxy transparent. Without this additional help the light from the galaxy, no matter how brilliant, would have been trapped in the surrounding hydrogen fog and we would not have been able to detect it.”

Sources: ESO, press briefing

Telescopes Open Up the Jewel Box

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Nothing in my jewelry box compares to the Kappa Crucis Cluster, also known as NGC 4755 or simply the “Jewel Box.” This object is just bright enough to be seen with the unaided eye, but a combination of images taken by three exceptional telescopes, the Very Large Telescope, the 2.2-meter telescope at the La Silla observatory and the Hubble Space Telescope, has allowed the stunning Jewel Box star cluster to be seen in a whole new light. Above is the image from ESO’ Very Large Telescope, which zooms in for a close look at the cluster itself. This new image is one of the best ever taken of this cluster from the ground, taken with an exposure time of just 5 seconds.

A Hubble gem: the Jewel Box.  Credit: NASA/ESO
A Hubble gem: the Jewel Box. Credit: NASA/ESO

The Hubble Space Telescope can capture light of shorter wavelengths than ground-based telescopes can, and this new HST image of the core of the cluster represents the first comprehensive far ultraviolet to near-infrared image of an open galactic cluster. It was created from images taken through seven filters, allowing viewers to see details never seen before. It was taken near the end of the long life of the Wide Field Planetary Camera 2, Hubble’s workhorse camera up until the recent Servicing Mission, when it was removed and brought back to Earth, and replaced with an new and improved version. Several very bright, pale blue supergiant stars, a solitary ruby-red supergiant and a variety of other brilliantly colored stars are visible in the Hubble image, as well as many much fainter ones. The intriguing colors of many of the stars result from their differing intensities at different ultraviolet wavelengths.

Wide Field Image  of the Jewel Box.  Credit:  ESO
Wide Field Image of the Jewel Box. Credit: ESO

A new image taken with the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile shows the cluster and its rich surroundings in all their multicolored glory. The large field of view of the WFI shows a vast number of stars. Many are located behind the dusty clouds of the Milky Way and therefore appear red.

Composite image of the Jewel Box. Credit: ESO
Composite image of the Jewel Box. Credit: ESO

Star clusters are among the most fascinating objects in the sky. Open clusters such as NGC 4755 typically contain anything from a few to thousands of stars that are loosely bound together by gravity. Because the stars all formed together from the same cloud of gas and dust their ages and chemical makeup are similar, which makes them ideal laboratories for studying how stars evolve.

Source: ESO