SD: Precisely Calculating the Age of Stars

[bystander]

Precisely Calculating the Age of Stars: Key to Evolution of a Type of White Dwarf Found
Science Daily - 13 May 2010

An international team of scientists has precisely calculated the age of a group of white dwarf stars. The research results open up new opportunities for advancing our understanding of the evolution of stars, plasma physics, and the origin of the universe in general.

A team of scientists ... has demonstrated that the white dwarf stars in the NGC 6791 star cluster are 8 billion years old, not 6 billion as previously believed. The research opens up new opportunities for extending our knowledge of the origin of the universe. ...

The researchers calculated the evolution of the white dwarfs from their birth to the present. Their calculations provide experimental confirmation of theories that have been proposed, but which up until now have not been corroborated by observational evidence. Specifically, the researchers have shown that sedimentation of the heaviest elements (under the strong gravity of the stars) and crystallization of material (due to the enormous pressure) take place in the interior of white dwarfs. These physical processes release energy inside the white dwarfs and slow their evolution. If they are properly taken into account, the age of stars of this type can be calculated with precision.

For years scientists have used the age of white dwarfs to estimate the age of the galaxy and other star systems. Their estimates of the age of these stars were based on theoretical considerations, but the level of uncertainty was very high because the occurrence of sedimentation and crystallization in the interior of white dwarfs could not be demonstrated. Up until now the proposed theories had not been independently verified based on observational data because in Earth-bound laboratories it is impossible to achieve the extremely high densities and temperatures that exist inside the stars (i.e., pressures of millions of grams per cubic centimeter and temperatures of millions of degrees). The calculations of this group of researchers were found to coincide with measurements of the age of NGC 6791 based on images taken by the Hubble Space Telescope.

Scientists from the UPC Barcelona Tech have precisely calculated the age of the stars
Universitat Politècnica de Catalunya Barcelona Tech (UPC Barcelona Tech) - 12 May 2010

A group of scientists led by the UPC has calculated white dwarf stars to be 8 billion years old. The research results will be published in the prestigious scientific journal 'Nature'.

The research opens up new opportunities for extending our knowledge of the origin of the universe.

True Age of Dying Stars Revealed by New Model
Space.com - 13 May 2010

Aging white dwarf stars may be coy about revealing their true age to astronomers, but a new computer simulation has finally unmasked the deception that allows such dwarfs to appear younger by shining more brightly.

A white dwarf cooling age of 8 Gyr for NGC 6791 from physical separation processes

• Nature Volume: 465, Pages: 194–196, (13 May 2010), DOI: 10.1038/nature09045

[bystander]

What's My Age? Mystery Star Cluster Has 3 Different Birthdays
Hubble Site - STScI-2008-25 - 10 July 2008

Imagine having three clocks in your house, each chiming at a different time. Astronomers have found the equivalent of three out-of-sync "clocks" in the ancient open star cluster NGC 6791. The dilemma may fundamentally challenge the way astronomers estimate cluster ages, researchers said.

Using NASA's Hubble Space Telescope to study the dimmest stars in the cluster, astronomers uncovered three different age groups. Two of the populations are burned-out stars called white dwarfs. One group of these low-wattage stellar remnants (red circles) appears to be 6 billion years old, another (blue circles) appears to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old.

White Dwarf Stars in Open Cluster NGC 6791
(NASA/ESA/DSS/STSci-L. Bedin)

In studying the dimmest burned-out stars in globular star cluster NGC 6791, NASA's Hubble Space Telescope has uncovered a paradox: three different populations of stars exist in an object where all the stars should have formed at the same time out of an interstellar cloud of gas and dust.

[Left] — This is a ground-based telescopic view of NGC 6791, located 13,300 light-years away in the constellation Lyra. The green inset box shows the view with Hubble's Advanced Camera for Surveys.

[Top right] — The full Hubble Advanced Camera for Surveys field is full of stars estimated to be 8 billion years old. Two background galaxies can be seen at upper left.

[Bottom right] — A blow up of view of a small region of the Advanced Camera for Surveys field reveals very faint white dwarfs. The blue circles identify hotter dwarfs that are 4 billion years old. The red circles identify cooler dwarfs that are 6 billion years old.

What's My Age? Mystery Star Cluster Has 3 Different Birthdays
ScienceDaily (11 July 2008)

Age of mystery star cluster unknown: NGC 6791 has three different birthdays.
Astronomy.com (11 July 2008)

How Old Am I? Star Cluster Perplexes Astronomers
Universe Today (10 July 2008)

[rstevenson]

Science Daily said, "A team of scientists ... has demonstrated that the white dwarf stars in the NGC 6791 star cluster are 8 billion years old, not 6 billion as previously believed."

This APOD, from 2000, also says the stars in this cluster are 8 billion years old. Another sign of a time traveller at work?

Rob

[bystander]

No, the problem wasn't with the age of the cluster, it was the age of the white dwarfs in the cluster.

Imagine having three clocks in your house, each chiming at a different time. Astronomers have found the equivalent of three out-of-sync "clocks" in the ancient open star cluster NGC 6791. The dilemma may fundamentally challenge the way astronomers estimate cluster ages, researchers said.

Using NASA's Hubble Space Telescope to study the dimmest stars in the cluster, astronomers uncovered three different age groups. Two of the populations are burned-out stars called white dwarfs. One group of these low-wattage stellar remnants (red circles) appears to be 6 billion years old, another (blue circles) appears to be 4 billion years old. The ages are out of sync with those of the cluster's normal stars, which are 8 billion years old.

The new research model provides an alternative explanation to to the ages of the white dwarfs.