Stars reveal the secrets of looking young

Dec 19, 2012
This image from the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile shows NGC 6388, a dynamically middle-aged globular cluster in the Milky Way. While the cluster formed in the distant past (like all globular clusters, it is over ten billion years old), a study of the distribution of bright blue stars within the cluster shows that it has aged at a moderate speed, and its heaviest stars are in the process of migrating to the center. A new study using ESO data has discovered that globular clusters of the same age can have dramatically different distributions of blue straggler stars within them, suggesting that clusters can age at substantially different rates. Credit: ESO, F. Ferraro (University of Bologna)

Some people are in great shape at the age of 90, while others are decrepit before they're 50. We know that how fast people age is only loosely linked to how old they actually are—and may have more to do with their lifestyle. A new study using both the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory and the NASA/ESA Hubble Space Telescope reveals that the same is true of star clusters.

Globular clusters are spherical collections of stars, tightly bound to each other by their mutual gravity. Relics of the early years of the Universe, with ages of typically 12-13 billion years (the took place 13.7 billion years ago), there are roughly 150 globular clusters in the and they contain many of our galaxy's oldest stars.

But while the stars are old and the clusters formed in the distant past, astronomers using the MPG/ESO 2.2-metre telescope and the /ESA have found that some of these clusters are still young at heart. The research is presented in the 20 December 2012 issue of the journal Nature.

"Although these clusters all formed billions of years ago," says Francesco Ferraro (University of Bologna, Italy), the leader of the team that made the discovery, "we wondered whether some might be aging faster or slower than others. By studying the distribution of a type of blue star that exists in the clusters, we found that some clusters had indeed evolved much faster over their lifetimes, and we developed a way to measure the rate of aging."

The aging of star clusters is linked more with their lifestyle than with how old they actually are, according to a new NASA/ESA Hubble Space Telescope study coauthored by Penn State astronomer Steinn Sigurdsson and other scientists, and led by Francesco Ferraro of the University of Bologna in Italy. The research reveals, for the first time, that each star cluster has its own internal clock, some of which are ticking slower than others. This image gallery shows 12 globular clusters ranked in order of increasing dynamical age as measured from the observed distribution of their blue-straggler stars. Credit: F. Ferraro (UniBO)

form in a short period of time, meaning that all the stars within them tend to have roughly the same age. Because bright, high-mass stars burn up their fuel quite quickly, and globular clusters are very old, there should only be low-mass stars still shining within them.

This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbour, or if they collide. The re-invigorated stars are called , and their high mass and brightness are properties that lie at the heart of this study.

Heavier stars sink towards the centre of a cluster as the cluster ages, in a process similar to sedimentation. Blue stragglers' high masses mean they are strongly affected by this process, while their brightness makes them relatively easy to observe.

To better understand cluster aging, the team mapped the location of blue straggler stars in 21 globular clusters, as seen in images from the MPG/ESO 2.2-metre telescope and Hubble, among other observatories. Hubble provided high resolution imagery of the crowded centres of 20 of the clusters, while the ground-based imagery gave a wider view of their less busy outer regions.

The aging of star clusters is linked more with their lifestyle than with how old they actually are, according to a new NASA/ESA Hubble Space Telescope study coauthored by Penn State astronomer Steinn Sigurdsson and other scientists, and led by Francesco Ferraro of the University of Bologna in Italy. The research reveals, for the first time, that each star cluster has its own internal clock, some of which are ticking slower than others. This illustration shows how blue-straggler stars become heavier than normal stars in star clusters. Blue stragglers are the result of stellar collisions (upper panel) or vampirism between two companion stars (lower panel). Credit: ESA Cosmic Lab

Analysing the observational data, the team found that a few clusters appeared young, with blue straggler stars distributed throughout, while a larger group appeared old, with the blue stragglers clumped in the centre. A third group was in the process of aging, with the stars closest to the core migrating inwards first, then stars ever further out progressively sinking towards the centre.

"Since these clusters all formed at roughly the same time, this reveals big differences in the speed of evolution from cluster to cluster," said Barbara Lanzoni (University of Bologna, Italy), a co-author of the study. "In the case of fast-aging clusters, we think that the sedimentation process can be complete within a few hundred million years, while for the slowest it would take several times the current age of the Universe."

As a cluster's heaviest stars sink towards the centre, the cluster eventually experiences a phenomenon called core collapse, where the centre of the bunches together extremely densely. The processes leading towards core collapse are quite well understood, and revolve around the number, density and speed of movement of the . However, the rate at which they happened was not known until now. This study provides the first empirical evidence of how quickly different age.

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More information: This research was presented in a paper, "Dynamical age differences amongst coeval star clusters as revealed by blue stragglers", by F. R. Ferraro et al., to appear in the journal Nature on 20 December 2012.

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Tuxford
1.3 / 5 (12) Dec 19, 2012
And why would heavier stars sink faster? Just because lighter stars get either destroyed or ejected? What is the reasoning?

Still, the distribution of blue stragglers varies in different clusters, but with most concentrated near the center of the cluster, still supports LaViolette's model. Those big blue stars experience accelerated growth from within, in the regions of higher mass density (more closely packed regions). I suspect that they will find that the denser the cluster, the more the blues are concentrated near the center.

http://phys.org/n...ter.html

Sedimentation? What is it? A sandpile?
Widdekind
1.6 / 5 (7) Dec 19, 2012
According to [1], BS form by head-on collisions & MERGERS; and by close encounters with MASS TRANSFER. The two types have slightly different properties. According to [2], head-on collisions are rarer than close encounters. According to [3], BS are concentrated in the cores of GC; and, there are two similar kinds of blue stars in GC, the other having seemingly formed from mass lost by other GC members. That may refer, to BS formed by head-on collisions, and others formed from not-quite-so-close encounters, which remove material from one star to another. According to [4], both "collisions" and "vampirism" co-occur in GCs. According to [1], aging GC eventually "core collapse", a dramatic densification of stars in GC centers.

[1] http://phys.org/n...tml#nRlv
[2] http://phys.org/n...tml#nRlv
[3] http://phys.org/n...ets.html
[4] http://phys.org/n...ars.html
Parsec
5 / 5 (5) Dec 19, 2012
Tuxford - think of a 3 body interaction where 2 bodies are considerably lighter than the other one. If you do the math, you will see that the most likely outcome is that the 2 lighter bodies will increase in velocity, and the heavier one will decrease. Thus, over time, the velocity of heavier stars tends to go down, which causes them to move closer to the center of gravity of the cluster.
Lurker2358
1 / 5 (4) Dec 20, 2012
1, Head on collision of two stars in the outer layers of the cluster.
2, the new star is more massive, in spite of likely having exploded from the impact.
3, The new star does not have enough relative velocity to maintain a stable orbit, so it's orbit decays inward.
4, It reaches the core and collides with other material there, forming a black hole.
5, If it hit anything else along the way it only serves to speed up the process.
6, When you move matter with some relative velocity into a head on collision, and then that matter sinks to the core, it increases the net gravity felt by each other layer below it's original layer of orbits. Now all of the other orbits begin to decay inward, eventually.
Widdekind
1 / 5 (6) Dec 20, 2012
3, The new star does not have enough relative velocity to maintain a stable orbit, so it's orbit decays inward.


such seems potentially important -- collisions & close-encounters might be dissipative processes, converting (kinetic) energy, into heat. If angular momentum was conserved, whilst energy was dissipated, then orbits would tend to circularize, circular orbits having the least energy per angular momentum. Collisions of stars, in clusters, could have similar effects, to collisions of proto-planets, in proto-planetary systems

-----------------------

Gravitational segregation, in star clusters, is often likened to that occurring within worlds. So, perhaps the "suddenness" of core collapse in the former, implies a similar threshold for the latter? And if "sudden" gravity effects occur within worlds, then perhaps something vaguely similar occurs within Neutron Stars, accounting for pulsar glitches? If so, then old, glitch'ed pulsars, are more segregated & sph.symmetric
clay_ferguson
1 / 5 (7) Dec 20, 2012
Seems to me like the 'age' that something would appear to us, no matter WHAT it is, could only be determined by integrating over time, the amount of mass it has been in the vicinity of (or contains even), and also added on to that, the amount of time it has spent at a velocity near light relative to the earth. For example, if you fly in a spaceship close enough to a large mass, you will basically stop aging. To me young looking clusters would just look young because they made a chance fly-by of a large mass like even the black hole in the center of our galaxy.

BTW: wikikind and lurker, congrats for understanding some of how gravity works. It's just a 'clumping' force isn't it. Thanks for describing that.
clay_ferguson
1 / 5 (8) Dec 20, 2012
I bet if they were to back-extrapolate the positions of all those 'young' clusters there would be at least one point of intersection of their paths, and that intersection would be where we would expect to find some large mass.
kevinrtrs
1 / 5 (13) Dec 20, 2012
Although these clusters all formed billions of years ago,"

There are some very questionable assumptions made in this article.
Firstly, just how do the researchers KNOW that globular clusters are very old?
They have based this conclusion on unjustifiable assumptions of
the accepted cosmological model.
Right now, there's only clear observational evidence that most clusters contain blue stars - which defies ANY notion of great age of the globular clusters.
So no matter how they try to slice and dice the observations into a progressive, dynamic aging process, the fact of the matter is that no one has lived to observe the creation of these clusters and blue stars, so no one has any documented evidence that they are old and progressively aging as assumed above.

Unless someone is going to live the supposed millions of years to observe how blue stars age and die, all of the above reasoning is pure speculation at this point. No matter how people want it otherwise.
kevinrtrs
1 / 5 (13) Dec 20, 2012
This, however, turns out not to be the case: in certain circumstances, stars can be given a new burst of life, receiving extra fuel that bulks them up and substantially brightens them. This can happen if one star pulls matter off a close neighbour, or if they collide

They do NOT know the history of these stars, so cannot make these leaps in logic. Even if we can currently observe stars feeding on matter from another, it is not justifiable to say that the stars were "old" [i.e. not BLUE] before we observed them - we just do not have any supporting older observations to jump to this conclusion.
kochevnik
3.4 / 5 (10) Dec 20, 2012
@kevinrtrs ...we just do not have any supporting older observations to jump to this conclusion.
YOU don't. WE do.
Shinobiwan Kenobi
2.8 / 5 (13) Dec 20, 2012
...the fact of the matter is that no one has lived to observe the creation of these clusters and blue stars, so no one has any documented evidence that they are old and progressively aging as assumed above.

Unless someone is going to live the supposed millions of years to observe how blue stars age and die, all of the above reasoning is pure speculation at this point. No matter how people want it otherwise.
Kev

How is it that you can spout this drivel and at the same time believe what is written in a 2000 year old collection of mistranslated faerie stories by people that never lived in the time that they are chronicling is true?

If your goal is to counter factual observation it would help if you actually made (or at least reference) factual observations to the contrary of that which you are attempting to counter; you probably wouldn't be so easily dismissed as a result.
RealScience
5 / 5 (6) Dec 20, 2012
@Kevin - the basic scientific method that lead to current understanding of stellar ages, cluster dynamics, etc. is the SAME METHOD that gave us the understanding of electricity, semiconductors, etc. needed to build computers and the internet.

So it you don't trust the results of science, please be consistent and STOP USING YOUR COMPUTER since it, too, is the result of science. Until then you are being hypocritical,

You are also being disrespectful. I'm sure that people here don't go onto religious site and spam them with science, so please give us the same courtesy on our science site and keep your non-science off.

Stop being a disrespectful hypocrite.
Fleetfoot
5 / 5 (2) Dec 25, 2012
And why would heavier stars sink faster? Just because lighter stars get either destroyed or ejected? What is the reasoning?


It is a consequence of the Virial Theorem.

http://en.wikiped..._theorem

Sedimentation? What is it? A sandpile?


Kinetic energy depends on mass so for a given (mean) energy, more massive stars have lower speeds hence tend to spend more time in the centre.
ValeriaT
1 / 5 (5) Dec 25, 2012
it you don't trust the results of science, please be consistent and STOP USING YOUR COMPUTER since it, too
With the same logics I could ask you to stop to use the inventions of Nazi Germany, if you don't trust the Nazis...;-) Actually just the lack of trust is the basis of scientific approach, which is based on falsification. The religion is based on the trust instead.
Torbjorn_Larsson_OM
5 / 5 (1) Jan 25, 2013
Creationists shouldn't comment on science. It is hilarious and makes deconverts from religion, see Dawkins's Convert's Corner.

Stars are age determined astronomically by star models, clusters aging by dynamical models as in teh article, and the standard cosmology constraints (not "assumptions", which science doesn't do) are justified by the observations that identifies them.