The view from inside a globular cluster has been the subject of recent speculation here, and I figure the man to imagine it is the gifted space artist Jon Lomberg. My new goal is to convince Jon to paint such a scene. They’re surrounded by beauty, as Jon’s painting would surely show, but would planets in these ancient clusters be inhabitable? Perhaps, but the stars in a cluster like M15 should also be ancient and metal-poor, meaning that planets around them may well be barren of life.
In astronomical terms, anything heavier than hydrogen and helium is a metal, and it’s long been thought that supernovae explosions are what spewed abundant metals out into the universe, resulting in more robust stars and solar systems like our own, where interesting chemical bonds begin to form. Hence the famous Saganism: ‘We are star-stuff.’
But new work at the University of Minnesota now points to an even richer conclusion. Using the Spitzer Space Telescope, a team led by Charles Woodward and Martha Boyer has found dust in M15, a cluster fully 12.5 billion years old.
Image: These false color images from Spitzer reveal a large dust cloud in the Globular Cluster M15 (in red). The left image was taken with a detector that is sensitive only to the hot emission from stars, and the right was taken with a detector that is sensitive to cooler dust emission. This is the first time that dust has been imaged in a globular cluster. Credit: M. Boyer, C. Woodward, University of Minnesota.
How did these ancient stars produce their dust in a metal-poor environment? Carbon, oxygen and nitrogen — metals all — are thought necessary to form the nuclei of the particles on which other elements condense to form dust grains. But Woodward’s team has been studying how metal-poor stars die, thinking that what little carbon they do produce does in fact go into a relatively efficient mechanism for seeding surrounding space with dust.
“Our work with globular clusters may show that dust can be made efficiently by these ordinary stars, even though they lack heavy metals,” said Boyer. “Then, perhaps, this dust combines with interstellar gas to form new stars and planets. About 13 billion years ago, most stars may have been like these, only not in clusters but everywhere, spewing out dust when they got old and turned into red giants.”
Thus newly forming solar systems emerge in an environment already affected by dust from both supernovae and smaller, older stars similar to those that can be observed today in M15. These older stars, in many respects like our Sun, never attain supernova status, but swell at the end of their lives into red giants, in Woodward’s view releasing carbon into the local neighborhood. A lack of oxygen in these stars allows the carbon to remain intact rather than turning into carbon monoxide, as it would in a star with higher metal content. And that carbon just may be the missing factor in creating the cluster’s interstellar dust.
Star-stuff? You bet. But factor vast, swelling red giants into our heritage as well as cataclysmic supernovae. The seeding of the universe with metals turns out to be more complicated than first imagined.
What fascinating work! Still, I would like to know if the dust in globular clusters has a chance to “coagulate” into a solar system. From what I understand, most star formation (and probably planet formation as well) occurs in regions of the galaxy where dust can accumulate over time into nebulae. Do these regions exist in globular clusters, or are they forever disrupted by the high densities (and I assume high space velocities) of neighboring stars? Since globular clusters spend much of their lives in the lonely vastness of the galactic halo, isn’t most of their dust simply ejected into the surrounding void?
A good question, and I have to defer to readers more familiar with globular clusters for comment. My hunch is that we’re too early in the study of dust in these clusters to know the answer, but maybe someone else can chime in.
great article,but funny thing…under seperate cover i had just asked if globular star clusters could be considered as other galaxies. i mean any massive group of stars out there on its own cetainly seems to qualify.we have ALOT to learn about this universe,as for me lol,probably twice as much! comments from everyone or anyone gladly accepted . your friend george scaglione
I’ll try to address both comments. First, GCs aren’t quite galaxies in their own right, but many astronomers believe that they could be the cores of old dwarf galaxies. Large GCs, like Omega Centauri and 47 Tuc show evidence of such a past. Second, the dust that is lost by stars in GCs doesn’t have a chance to form planets in the GC itself, because one needs dust to be present at the beginning of star birth in order to form planets along with the stars. Since this dust wasn’t expelled until the ending stages of a star’s life (after all star formation has ceased), it is stuck in the void of the cluster. However, it eventually enters our galaxy’s disk, where there is star formation going on & it can help form planets. It could still be that there are planets in GCs, but I would guess that there are very few, as not much dust existed in the universe at the time of GC formation.
Thank you for clarifying these issues. And thank you and Dr. Woodward as well for this work on dust in M15, which has brought a crucial mechanism of dust formation to light. It becomes clear that metals forged in supernovae aren’t the only way to seed surrounding space with the materials needed for new star and planet formation.
thank you very much martha i appreciate your time! so… then i will take it that gobular clusters are a different type of structure in the universe,a free standing seperate entity.thank you again, george
Alpha Centauri – I can picture the wo stars orbiting eachother. But I don’t understand the third star ? .1 Light year farther away ? Is it not part of the same solar system.How could it always be farther away ? Also I understand we now have a few stars older than the Big Bang ?? Opps ! Another calculation way off ?
Bob, the third star, Proxima Centauri, is about 10,000 AU away — in other words, 10,000 times as far from the other two as the Earth is from the Sun. But recent research does indicate that it is part of the Alpha Centauri system, and may have an effect on disrupting the outer debris disk enough to send comets and other materials to the inner system. Here’s a previous article about this:
https://centauri-dreams.org/?p=726
Hi Bob
The Universe is believed to be 13.7 billion years old and the oldest stars about 13.6 billion. Thus a GC that’s 12.5 billion is no big deal. Paul’s quite right about Proxima Centauri being a (possible) member of the Alpha Centauri A & B binary, though as yet the data has enough room to move that Proxima might be orbitting them or might be just flying by. Over the next few years hopefully someone will have a closer look.
Adam
I’ll disagree with Adam slightly on that. I think Proxima’s status was much less clear before Laughlin and Wertheimer’s recent work. Their findings imply a gravitational connection and provide an interesting surmise about habitability of planets around Centauri A and B. I think the pendulum is swinging back to the idea that this is a triple system.
These are NOT facts, but questions—>Electrons & protons have opposite charges and resist becoming elements ? Hydrogen and heavy H was created by the Big Bang explosion ?? Helium is formed in the core of our yellow sun by pressing two H atoms together ?? It takes 1000 years for a He atom to squeeze it’s way from the center of the sun to the outer skin ? At the end of our suns life it will be a red giant where it has enough pressure to make Carbon somehow ? If our sun would have had 5-10 times greater mass it would have been a blue giant with a short life ?? And when this blue giant dies, the pressure from the Super Nova explosion is enough to press H and He into most of the other naturally occuring elements ??
Hi Bob
What’s your point?
Most of the work on nucleosynthesis inside old stars is pretty well established, though the data on some fusion-chain rates could be better. As for H/He “pressing into” each other – fusion is about overcoming Coulomb repulsion, yes, but it’s also about the attraction of the nuclear force when the potential barrier is overcome. Quantum Tunnelling is what makes nuclear fusion viable in stars below a central temperature of a billion degrees or so.
And it’s not really “pressure” in a supernova that matters, but energy – an immense amount of gravitational energy is released as heat in the iron core of a supernova progenitor as it collapses into a slurry of neutrons. At least that’s what happens in a Core-Collapse supernova. Other types exist, like when a white dwarf erupts as a gigantic fusion bomb.
Globular clusters with the extended horizontal-branch as remaining cores of galaxy building blocks
Authors: Young-Wook Lee, Hansung B. Gim, Chul Chung
(Submitted on 11 Jul 2007)
Abstract: The relics of building blocks that made stellar halo and bulge are yet to be discovered unless they were completely disrupted throughout the history of the Galaxy. Here we suggest that about 25% of the Milky Way globular clusters have characteristics of the remaining cores of these early building blocks rather than genuine star clusters. They are clearly distinct from other normal globular clusters in the presence of extended horizontal-branch and multiple stellar populations, in mass (brightness), and most importantly in orbital kinematics. Based on this result, a three-stage formation picture of the Milky Way is suggested, which includes early mergers, collapse, and later accretion.
Comments: Invited paper presented at the conference “New Quests in Stellar Astrophysics II: Ultraviolet Properties of Evolved Stellar Populations”, M. Chavez, E. Bertone, D. Rosa-Gonzalez, & L. H. Rodriguez-Merino eds
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0707.1705v1 [astro-ph]
Submission history
From: Young-Wook Lee [view email]
[v1] Wed, 11 Jul 2007 20:56:00 GMT (33kb)
http://arxiv.org/abs/0707.1705
Will asteriod-mining ever become economical ? Or will it always be cheaper to find new iron and nickel here on earth ? Is it possible there are materials on asteroids that woud be mining, like the He3 on the moon ?
Unusual supernovae may reveal intermediate-mass black holes in globular clusters
For Immediate Release
SANTA CRUZ, CA–A strange and violent fate awaits a white dwarf star that
wanders too close to a moderately massive black hole. According to a new study,
the black hole’s gravitational pull on the white dwarf would cause tidal forces
sufficient to disrupt the stellar remnant and reignite nuclear burning in it,
giving rise to a supernova explosion with an unusual appearance. Observations of
such supernovae could confirm the existence of intermediate-mass black holes,
currently the subject of much debate among astronomers.
“Our supercomputer simulations show a peculiar supernova that would be a unique
signature of an intermediate-mass black hole,” said Enrico Ramirez-Ruiz,
assistant professor of astronomy and astrophysics at the University of
California, Santa Cruz.
Ramirez-Ruiz and his collaborators–Stephan Rosswog of Jacobs University in
Bremen, Germany, and William Hix of Oak Ridge National Laboratory–used detailed
computer simulations to follow the entire process of tidal disruption of a white
dwarf by a black hole. Their simulations included gas dynamics, gravity, and
nuclear physics, requiring weeks of computer time to simulate events that would
take place in a fraction of a second. A paper describing their results has been
accepted for publication in Astrophysical Journal Letters, and a preprint is
currently available online.
“Every star that is not too massive ends up as a white dwarf, so they are very
common. We were interested in whether tidal disruption can bring this stellar
corpse to life again,” said Rosswog, the first author of the paper.
A white dwarf can explode as a “type Ia” supernova if it accumulates enough mass
by siphoning matter away from a companion star. When it reaches a critical mass
(about 1.4 times the mass of the Sun), the white dwarf collapses and explodes.
Astronomers use these type Ia supernovae as “standard candles” for cosmic
distance measurements because their brightness evolves over time in a
predictable manner.
The new paper describes a distinctly different mechanism for igniting a white
dwarf, in which tidal disruption by a black hole causes drastic compression of
the stellar material. The white dwarf is flattened into a pancake shape aligned
in the plane of its orbit around the black hole. As each section of the star is
squeezed through a point of maximum compression, the extreme pressure causes a
sharp increase in temperatures, which triggers explosive burning.
The explosion ejects more than half of the debris from the disrupted star, while
the rest of the stellar material falls into the black hole. The infalling
material forms a luminous accretion disk that emits x-rays and should be
detectable by the Chandra X-ray Observatory, the researchers said.
“This is a new mechanism for ignition of a white dwarf that results in a very
different type of supernova than the standard type Ia, and it is followed by an
x-ray source,” Ramirez-Ruiz said.
He estimated that this type of event would occur about 100 times less frequently
than the standard type Ia supernovae, but should be detectable by future surveys
designed to observe large numbers of supernovae. The Large Synoptic Survey
Telescope (LSST), planned for completion in 2013, is expected to discover
hundreds of thousands of type Ia supernovae per year.
“These exotic creatures will start showing up in the data from the LSST,”
Ramirez-Ruiz said. “We want to predict the light curves so we can look for them
in the survey data.”
The mechanism described in the paper requires a black hole that is neither too
small nor too big. Such intermediate-mass black holes (500 to 1,000 times the
mass of the Sun) may reside in some globular star clusters, but there is much
less evidence for their existence than there is for the relatively small stellar
black holes (tens of times the mass of the Sun) or for supermassive black holes
(a few million times the mass of the Sun), found at the centers of galaxies.
The new paper describes in detail the disruption of a white dwarf with
two-tenths the mass of the Sun by a black hole 1,000 times the mass of the Sun.
The researchers also found that they can vary the mass of the white dwarf and
still get the same outcome–tidal disruption and ignition of the white dwarf.
“We can ignite the whole mass range of white dwarfs if they get close enough to
the black hole,” Rosswog said.
This research was supported by the Department of Energy’s Program for Scientific
Discovery through Advanced Computing.
#####
Note to reporters: You may contact Ramirez-Ruiz at 1-831-459-3400 or
enrico@ucolick.org
An extended star cluster at the outer edge of the spiral galaxy M33
Authors: Rima Stonkute (1), Vladas Vansevicius (1), Nobuo Arimoto (2 and 3), Takashi Hasegawa (4), Donatas Narbutis (1), Naoyuki Tamura (5), Pascale Jablonka (6), Kouji Ohta (7), Yoshihiko Yamada (2) ((1) Inst. of Phys., Lithuania, (2) Nat. Astr. Obs. of Japan, (3) Dept. of Astr. Grad. Univ. of Adv. Studies, Japan, (4) Gunma AO, Japan, (5) Subaru Tel. Obs., Japan (6) Univ. de Geneve, Switzerland, (7) Kyoto Univ., Japan)
(Submitted on 4 Feb 2008)
Abstract: We report a discovery of an extended globular-like star cluster, M33-EC1, at the outer edge of the spiral galaxy M33. The distance to the cluster is 890 kpc, and it lies at a 12.5 kpc projected distance from the center of M33. Old age (greater than ~7 Gyr) and low metallicity ([M/H] less than ~ -1.4) are estimated on the basis of isochrone fits. Color-magnitude diagrams of stars, located in the cluster’s area, photometric and structural parameters of the cluster are presented. Cluster’s luminosity (M_V = -6.6) and half-light radius (r_h = 20.3 pc) are comparable to those of the extended globular clusters, discovered in more luminous Local Group galaxies, the Milky Way and M31.
Extended globular clusters are suspected to be remnants of accreted dwarf galaxies, and the finding of such a cluster in the late-type dwarf spiral galaxy M33 would imply a complex merging history in the past.
Comments: 20 pages, 6 figures, 2 tables, accepted for publication in AJ
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0802.0501v1 [astro-ph]
Submission history
From: Rima Stonkute [view email]
[v1] Mon, 4 Feb 2008 21:02:47 GMT (360kb)
http://arxiv.org/abs/0802.0501
Clearing the Dust from Globular Clusters
Authors: Stefan Umbreit, Sourav Chatterjee, Frederic A. Rasio
(Submitted on 15 May 2008)
Abstract: Recent Spitzer observations of the globular cluster M15 detected dust associated with its intracluster medium. Surprisingly, these observations imply that the dust must be very short-lived compared to the time since the last Galactic plane crossing of the cluster.
Here we propose a simple mechanism to explain this short lifetime. We argue that the kinetic energy of the material ejected during a stellar collision may be sufficient to remove the gas and dust entirely from a cluster, or to remove the gas as a wind, in addition to partially destroying the dust. By calculating the rate of stellar collisions using an N-body model for the cluster, we find remarkable agreement between the average time between collisions and the inferred dust lifetime in this cluster, suggesting a possible close relation between the two phenomena.
Furthermore, we also obtain the birthrate of blue stragglers formed through collisions in M15. By comparing with the observed number of blue stragglers, we derive an upper limit for their average lifetime which turns out to be consistent with recent model calculations, thereby lending further support to our model.
Comments: 4 pages, 1 figure, to appear in ApJ Letters
Subjects: Astrophysics (astro-ph)
Cite as: arXiv:0805.2358v1 [astro-ph]
Submission history
From: Stefan Umbreit [view email]
[v1] Thu, 15 May 2008 17:04:07 GMT (13kb)
http://arxiv.org/abs/0805.2358
http://apod.nasa.gov/apod/ap110503.html
Globular Cluster M15 from Hubble
Credit: ESA, Hubble, NASA
Explanation: Stars, like bees, swarm around the center of bright globular cluster M15. This ball of over 100,000 stars is a relic from the early years of our Galaxy, and continues to orbit the Milky Way’s center. M15, one of about 150 globular clusters remaining, is noted for being easily visible with only binoculars, having at its center one of the densest concentrations of stars known, and containing a high abundance of variable stars and pulsars.
This sharp image, taken by the Earth-orbiting Hubble Space Telescope, spans about 120 light years. It shows the dramatic increase in density of stars toward the cluster’s center. M15 lies about 35,000 light years away toward the constellation of the Winged Horse (Pegasus). Recent evidence indicates that a massive black hole might reside as the center of M15.