Did Giant Stars Feed Blue Stragglers?

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In a letter to the journal Nature published this week, astronomers Aaron Geller and Robert Mathieu offer an explanation for the origin of blue straggler stars in a star cluster called NGC 188. Geller suggests the stars fed on neighbor stars, leaving behind white dwarfs.

Copyright © 2011 National Public Radio®. For personal, noncommercial use only. See Terms of Use. For other uses, prior permission required.

IRA FLATOW, host: This is SCIENCE FRIDAY. I'm Ira Flatow. If you take a telescope, and you trained it on a cluster of stars, you're looking at a group of stars that formed at about the same time, but they may not all look the same. In some clusters, astronomers have caught a glimpse of some stars that stand out from the others: They burn bluer and brighter, they seem to be younger than they should be. They're called Blue Stragglers.

There are a couple of theories about how Blue Stragglers form. Are they the result of collisions between two stars? Or maybe they came from a merger of stars. Writing this week in the journal Nature, my next guest offers his theory on the origin of Blue Stragglers. Aaron Geller is Postdoctoral Fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois. Thanks for being with us today, Dr. Geller.

Dr. AARON GELLER: My pleasure, thanks for having me.

FLATOW: Tell us about - what is a Blue Straggler, and why should we care about it?

GELLER: Well, like you say, Blue Stragglers are stars that we observe to be bluer and brighter than normal stars of similar mass and age. But let me give you a little context for that definition. And normal stars - well, normal stars for instance like our sun - they spend most of their lives having a very similar size and temperature.

And then at a certain point, toward the end of their lives, they become much bigger, up to 100 times the size, and become what we call giant stars. Even later on, they die and become stellar remnants, and for a star like our sun, that would be a white dwarf.

Now, we can predict how long it should take for a normal star to go from, you know, being this normal, kind of steady state, to becoming a giant. And when we look at Blue Stragglers, we see that they are - they have somehow maintained this normal state for longer than we would have expected.

Now physically, we think that this is because Blue Stragglers have gained some extra material from another star, and this extra mass has allowed the Blue Straggler to become bluer and brighter, and therefore it looks younger, if you will, than we should expect.

And this is basically why we call them stragglers, because they're in a sense straggling behind all the other stars that they grew up with in terms of star evolution.

FLATOW: And so what's the mystery about them?

GELLER: Well, they were discovered some 60 years ago, and you mentioned a few of the theories about where they come from. There have been a lot of other theories along the way, as well. And the three that have really survived scientific scrutiny is collisions, like you said; mergers; and also mass transfer.

And so the mystery is really which one of these is really the dominant way of making these Blue Stragglers in certain different environments. And we studied a star cluster, NGC188, and we were trying to determine where these Blue Stragglers came from.

FLATOW: And you discovered - which one of your theories is correct, then, that it sucks up other stuff?

GELLER: So yes, the theory that we think is the - explains most of the Blue Stragglers in our cluster is called mass transfer. And let me explain what that is. You start out with two stars that are in a binary system, so they're orbiting each other. One of the stars evolves to become a giant, like I was explaining before, and they are close enough together that the outer material from this giant star gets, like you were saying, sucked on to the other star, and this other star eventually consumes all of the outer material from the giant and becomes a Blue Straggler.

And in doing so, it - all that's left of the giant is the core of that star, which is a white dwarf. So you're left with a Blue Straggler that has a binary companion that is a white dwarf, and this is what we think we observe in NGC188.

FLATOW: Can we actually see any - if we had our, you know, our backyard telescope out or our binoculars?

GELLER: Well, you could see the Blue Straggler stars. These would be some of the bluest stars and brightest stars in the cluster. Now, you could not see with your telescope the white dwarf companion. It turns out that white dwarfs don't emit very brightly in optical light, in visible, that we can see.

In fact, the Blue Straggler is much brighter than the white dwarf. But if you were to switch to a different wavelength range, for instance the ultraviolet, then the white dwarf is actually quite bright in comparison to the Blue Straggler, and that is when you can actually potentially see these white dwarfs. And this is a project that my collaborator Bob Matthew(ph) and a few others are involved with to get ultraviolet images of these Blue Stragglers with the Hubble Space Telescope.

FLATOW: And what more would you like to learn about all this?

GELLER: Well, there is still a few - so we've looked at many of the Blue Stragglers in NGC188 and said that most of these look like they come from mass transfer, but that's not the whole story. There are still some other Blue Stragglers in the cluster that we don't know very much about, and of course I would love to get the confirmation on these Blue Stragglers that we have studied with the Hubble data. I would love to see the white dwarfs myself.

FLATOW: Why do you call them Blue Stragglers? That's such a demotion it sounds to me of the victorious star.

(SOUNDBITE OF LAUGHTER)

GELLER: Well, it's true. I guess when they were first discovered, they weren't called Blue Stragglers. It wasn't until a few years later that someone coined that term. Well, they're blue.

FLATOW: Yeah, that we can buy.

GELLER: They're blue stars, and they seem like they are straggling behind normal stars. They're just not evolving as quickly as we would expect. So they look younger, and they're straggling.

FLATOW: And they're better well-fed, is what it is, from the other companion stars.

GELLER: They are indeed, and this actually brings up a funny kind of analogy that people have been throwing around with the Blue Stragglers formed by mass transfer. They're calling them stellar vampires because they feed off of their companions to make them look younger, which is, I guess, kind of timely since we're getting so close to Halloween.

FLATOW: And I certainly can't top that. So I'm going to let you go.

(SOUNDBITE OF LAUGHTER)

FLATOW: And thank you for taking time to be with us today, Dr. Geller.

GELLER: Thanks for having me.

FLATOW: Aaron Geller is the Lindheimer Postdoctoral Fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois.

Copyright © 2011 National Public Radio®. All rights reserved. No quotes from the materials contained herein may be used in any media without attribution to National Public Radio. This transcript is provided for personal, noncommercial use only, pursuant to our Terms of Use. Any other use requires NPR's prior permission. Visit our permissions page for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.

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Did Giant Stars Feed Blue Stragglers?

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In a letter to the journal Nature published this week, astronomers Aaron Geller and Robert Mathieu offer an explanation for the origin of blue straggler stars in a star cluster called NGC 188. Geller suggests the stars fed on neighbor stars, leaving behind white dwarfs.

Copyright © 2011 National Public Radio®. For personal, noncommercial use only. See Terms of Use. For other uses, prior permission required.

IRA FLATOW, host: This is SCIENCE FRIDAY. I'm Ira Flatow. If you take a telescope, and you trained it on a cluster of stars, you're looking at a group of stars that formed at about the same time, but they may not all look the same. In some clusters, astronomers have caught a glimpse of some stars that stand out from the others: They burn bluer and brighter, they seem to be younger than they should be. They're called Blue Stragglers.

There are a couple of theories about how Blue Stragglers form. Are they the result of collisions between two stars? Or maybe they came from a merger of stars. Writing this week in the journal Nature, my next guest offers his theory on the origin of Blue Stragglers. Aaron Geller is Postdoctoral Fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois. Thanks for being with us today, Dr. Geller.

Dr. AARON GELLER: My pleasure, thanks for having me.

FLATOW: Tell us about - what is a Blue Straggler, and why should we care about it?

GELLER: Well, like you say, Blue Stragglers are stars that we observe to be bluer and brighter than normal stars of similar mass and age. But let me give you a little context for that definition. And normal stars - well, normal stars for instance like our sun - they spend most of their lives having a very similar size and temperature.

And then at a certain point, toward the end of their lives, they become much bigger, up to 100 times the size, and become what we call giant stars. Even later on, they die and become stellar remnants, and for a star like our sun, that would be a white dwarf.

Now, we can predict how long it should take for a normal star to go from, you know, being this normal, kind of steady state, to becoming a giant. And when we look at Blue Stragglers, we see that they are - they have somehow maintained this normal state for longer than we would have expected.

Now physically, we think that this is because Blue Stragglers have gained some extra material from another star, and this extra mass has allowed the Blue Straggler to become bluer and brighter, and therefore it looks younger, if you will, than we should expect.

And this is basically why we call them stragglers, because they're in a sense straggling behind all the other stars that they grew up with in terms of star evolution.

FLATOW: And so what's the mystery about them?

GELLER: Well, they were discovered some 60 years ago, and you mentioned a few of the theories about where they come from. There have been a lot of other theories along the way, as well. And the three that have really survived scientific scrutiny is collisions, like you said; mergers; and also mass transfer.

And so the mystery is really which one of these is really the dominant way of making these Blue Stragglers in certain different environments. And we studied a star cluster, NGC188, and we were trying to determine where these Blue Stragglers came from.

FLATOW: And you discovered - which one of your theories is correct, then, that it sucks up other stuff?

GELLER: So yes, the theory that we think is the - explains most of the Blue Stragglers in our cluster is called mass transfer. And let me explain what that is. You start out with two stars that are in a binary system, so they're orbiting each other. One of the stars evolves to become a giant, like I was explaining before, and they are close enough together that the outer material from this giant star gets, like you were saying, sucked on to the other star, and this other star eventually consumes all of the outer material from the giant and becomes a Blue Straggler.

And in doing so, it - all that's left of the giant is the core of that star, which is a white dwarf. So you're left with a Blue Straggler that has a binary companion that is a white dwarf, and this is what we think we observe in NGC188.

FLATOW: Can we actually see any - if we had our, you know, our backyard telescope out or our binoculars?

GELLER: Well, you could see the Blue Straggler stars. These would be some of the bluest stars and brightest stars in the cluster. Now, you could not see with your telescope the white dwarf companion. It turns out that white dwarfs don't emit very brightly in optical light, in visible, that we can see.

In fact, the Blue Straggler is much brighter than the white dwarf. But if you were to switch to a different wavelength range, for instance the ultraviolet, then the white dwarf is actually quite bright in comparison to the Blue Straggler, and that is when you can actually potentially see these white dwarfs. And this is a project that my collaborator Bob Matthew(ph) and a few others are involved with to get ultraviolet images of these Blue Stragglers with the Hubble Space Telescope.

FLATOW: And what more would you like to learn about all this?

GELLER: Well, there is still a few - so we've looked at many of the Blue Stragglers in NGC188 and said that most of these look like they come from mass transfer, but that's not the whole story. There are still some other Blue Stragglers in the cluster that we don't know very much about, and of course I would love to get the confirmation on these Blue Stragglers that we have studied with the Hubble data. I would love to see the white dwarfs myself.

FLATOW: Why do you call them Blue Stragglers? That's such a demotion it sounds to me of the victorious star.

(SOUNDBITE OF LAUGHTER)

GELLER: Well, it's true. I guess when they were first discovered, they weren't called Blue Stragglers. It wasn't until a few years later that someone coined that term. Well, they're blue.

FLATOW: Yeah, that we can buy.

GELLER: They're blue stars, and they seem like they are straggling behind normal stars. They're just not evolving as quickly as we would expect. So they look younger, and they're straggling.

FLATOW: And they're better well-fed, is what it is, from the other companion stars.

GELLER: They are indeed, and this actually brings up a funny kind of analogy that people have been throwing around with the Blue Stragglers formed by mass transfer. They're calling them stellar vampires because they feed off of their companions to make them look younger, which is, I guess, kind of timely since we're getting so close to Halloween.

FLATOW: And I certainly can't top that. So I'm going to let you go.

(SOUNDBITE OF LAUGHTER)

FLATOW: And thank you for taking time to be with us today, Dr. Geller.

GELLER: Thanks for having me.

FLATOW: Aaron Geller is the Lindheimer Postdoctoral Fellow at the Center for Interdisciplinary Exploration and Research in Astrophysics at Northwestern University in Evanston, Illinois.

Copyright © 2011 National Public Radio®. All rights reserved. No quotes from the materials contained herein may be used in any media without attribution to National Public Radio. This transcript is provided for personal, noncommercial use only, pursuant to our Terms of Use. Any other use requires NPR's prior permission. Visit our permissions page for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR's programming is the audio.

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Sunny side serves massive stars

Researchers at the European Southern Observatory have discovered a huge, sunny side after top egg in space.

The fried egg - a massive star, surrounded by a double, the next yellow Hypergiant star neighboring Earth finds outer ring of gaseous dust - up today. Yellow hypergiants are rarely, massive stars living in a phase of the life cycle of a star, which only takes usually a couple hundred thousand years - a Flash in the life of the Galaxy. You consume a lot of energy to burn so bright.

Dust clouds surrounded the entire body of the Nebula - a yellow Hypergiant "Yolk" "Protein" - located about 13,000 light years from Earth.

"This object had glowing bright above noticed people, but nobody had identified it as a yellow Hypergiant," astronomer Eric Lagadec says, to examine part of European Southern Observatory team that discovered the monster star, while the neighboring stars.

The Nebula is massive: it has a radius of 10,000 times the distance from the earth around the Sun. For scaling, you would provide the Centre of the Nebula in the center of our solar system - the Sun - then the outermost part of the Nebula would reach star Jupiter. Of the regions in outermost part of the Nebula would some gaseous rings orbit Comet Neptune span.

The infrared photographs Lagadec and his colleagues in the fog with heavy duty telescope, used, to capture images. Above the photo shows the bright, shining star embedded in the middle of two outer shells of cosmic dust - gases the whole galaxy.

The outer rings of dust are the remains of the earlier explosions, has been through the star as it dies. Finally, the star in a supernova event, which all start his gaseous matter in the universe will explode. And when that happens, it is probably as bright as Venus lights and visible during the day, says Lagadec.

He says "It could happen tomorrow or in a few hundred thousand years".

This research was approved publication by the journal astronomy & Astrophysics.

View the original article here

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Here Come The Suns: New Planet Orbits Two Stars

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R. Hurt/NASA/JPL-Caltech

NASA's Kepler mission has discovered a planet that circles two stars instead of one. The planet, shown as the black dot in this artist's illustration, is similar to Saturn, though it is more dense and travels in a 229-day circular orbit around its two stars.

A trillion is a huge number — when you're talking dollars or euros. But a trillion miles is not so much in the cosmic scheme of things. Astronomers say they've now found a planet that orbits two suns a mere thousand trillion miles from here. It's yet another example of a weird solar system being discovered around nearby stars.

Two years ago, NASA launched the Kepler observatory to look for Earth-like planets beyond our own solar system. It has found more than 1,000 apparent planets around distant suns.

This animation shows the Kepler-16 system from an overhead view. The two stars in the center twirl around each other every 41 days while the planet, shown as the small white dot, makes a full circle around the stars every 229 days.
(Note: This video has no sound.)

This graphic requires version 9 or higher of the Adobe Flash Player.Get the latest Flash Player.

This animation shows the Kepler-16 system from an overhead view. The two stars in the center twirl around each other every 41 days while the planet, shown as the small white dot, makes a full circle around the stars every 229 days.
(Note: This video has no sound.)

Now, for the first time, it has found a planet in orbit around a double star. Laurance Doyle from the SETI Institute in California says these twin stars are 200 light-years away from us in the constellation Cygnus, and each one has a slightly different hue.

"You have an orange star that's 69 percent the mass of the sun, and it is basically dancing with a 20-percent-the-mass-of-the-sun red star," he says. "And they go around each other every 41 days."

Doyle and his many collaborators looked closely at this system and watched as the stars temporarily dimmed with a predictable pattern — a sure sign that a planet was passing in front of them. Astronomers had previously seen strong hints of planets around twin stars, but this is the first direct observation, according to their report in Science.

'A Giant Laboratory'

The planet, named Kepler-16b, orbits in a big circle every 229 days. It's a frozen world, about the size of Saturn, and it's likely a ball of gas with a rocky interior. But Doyle imagines the sunsets would be dramatic.

"I remember from Star Wars — Tatooine. Luke Skywalker was watching a double sunset. But in this case, sometimes you get a sunset where they're far apart and maybe the red star sets first, and maybe the next month the orange star sets first," he says. "And sometimes they set touching each other, sometimes they set eclipsing."

More dramatic to astronomers is that they can learn a lot about the stars and the planet as they dance around one another. The junior star in this system, for example, is the smallest normal star ever discovered, Doyle says. And the bigger star is outright perplexing.

"It rotates slowly, which indicates it's old, but it has large starspot activity, which is an indicator of youth," he says. "So the whole place is a giant laboratory."

One of the biggest conundrums is understanding the very existence of planets around twin stars, "because they shouldn't be there," says Dave Charbonneau, a professor of astronomy at Harvard University. He says the standard story is that planets form from a pancake-shaped disk of material that's left over after a singleton star coalesces.

"When you have a binary star — two stars that orbit each other — that pancake of material could be easily disrupted. And so we have a harder time actually figuring out how to make a planet so that it can be born and stably orbit two stars," Charbonneau says.

A New Horizon Of Twin Stars

Charbonneau was not involved with this particular discovery, but he says it shows clearly that planets can form around binaries. That opens up a whole new horizon in the search for planets because most stars are actually born as twins.

"So actually the sun is somewhat of a rarity from that perspective," he says. "Now what we want to know is: Do most binary stars have planets just like we now think that most single stars do? And I think the future data from the NASA Kepler mission is going to help sort that out."

In fact, Doyle estimates there are 2 million solar systems around twin stars in our galaxy. He's been hunting for them for 20 years, and all of a sudden, the Kepler observatory has made his quest so much easier. "Now that we know how to find them, I think within the next few months we're going to find a few more," he says. "It's a gift, you know. After 20 years, the universe finally said, 'Try this one.' "

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The twin stars are 200 light-years away from us, and each one has a slightly different hue.

The Space Launch System could take its first manned test flight in 2017.

The Space Launch System will cost about $35 billion and could start test launching in six years.

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HEALTH MANAGEMENT. Here come the Suns: new planet orbits two stars

R. hurt/NASA / JPL-Caltech
The Kepler mission NASA has discovered a planet, the two stars instead of a circle. Saturn is similar to the planet, as the black point in this artist's figure, although it more dense and travels in a 229-day circular orbit around the two stars.
A large number - is a trillion if you speak, dollars or euros. But a trillion miles is not so much in the cosmic order of things. Astronomers say that they have now found a planet orbiting two Suns a mere thousand trillion miles from here. It is yet another example of a strange solar system around nearby star discovered.
Ago launched to search two years NASA Kepler Observatory for Earth-like planet beyond our solar system. It has found more than 1,000 obvious planets around distant suns.
This animation shows the Kepler-16 system from an overhead view. The two stars in the Center Vortex around each other every 41 days during of the planet, as the small white point, makes a full circle around the star every 229 days.
(Note: this video has no sound.)
This graphic requires version 9 or higher of the Adobe Flash Player.Get the latest Flash Player.
This animation shows the Kepler-16 system from an overhead view. The two stars in the Center Vortex around each other every 41 days during of the planet, as the small white point, makes a full circle around the star every 229 days.
(Note: this video has no sound.)
Now, it has found a planet in orbit around a star for the first time. Laurance Doyle of the SETI Institute in California says these two stars are away in the constellation Cygnus 200 light years from Earth, and each has a slightly different color.
"You have an orange star, which is 69 percent, with the mass of the Sun, and it basically is the 20-percent-the-mass-of-the-sun red star dance", he says. "And they go all 41 days to each other."
Doyle and his this system closely looked many employees and saw how the star temporarily with a predictable pattern dimmed - a sure sign that a planet to them was passed. Astronomers had seen strong evidence of planets around two stars before, but this is the first direct observation, their report in science.
"A giant laboratory"
The planet, called Kepler-16 b, encircled in a big circle all 229 days. It is a cold planet, about the size of Saturn, and it is probably a ball of gas with a rocky Interior. But Doyle introduces himself, that the sunsets would be dramatic.
"I remember from Star Wars - Tatooine." Luke was Skywalker watch a double sunset. But in this case sometimes a sunset where they are far apart, and perhaps the first, and perhaps first sets Red Star sets the orange star in the next month, the, "he says." "And sometimes you put into each other, sometimes they eclipsing."
More dramatic opened astronomers is that they learn dance a lot about the stars and planets as they to each other. The junior star in this system is, for example, the smallest normal star that ever discovered, says Doyle. And the larger star is downright confusing.
"It slowly rotates, which means, it is old, but it has great Starspot activity, which is an indicator of the youth," he says. "The whole place is as a giant laboratory."
One of the greatest puzzles the existence of planets around two stars, understand "because she should be there", says Dave Charbonneau, Professor of astronomy at Harvard University. He says that is the standard history of this planet from a pancake-shaped disk of material left after a singleton star coalesces.
"If you have a star - two stars orbiting each other - the pancakes material could easily be disturbed." "And so we have a harder time actually find out, like a planet, so that they can be born and stable orbit two stars", Charbonneau says.
A new horizon of two stars
Charbonneau was not with this specific discovery, but he says that it shows clearly that the planets around binary files can make. She opened a whole new horizon in the search for planets, because most stars are actually born as twins.
"So actually the Sun a little is a rarity from this perspective," he says. "Now we want to know: the most double stars have planets as we now think that do single stars?" "And I think that the future data from NASA Kepler mission will help to clarify."
In fact, Doyle estimates that there are 2 million solar system to two stars in our galaxy. He has for them is hunting for 20 years, and suddenly, the Kepler Observatory his search so much easier. "Now that we know how to find, I think in the next few months are we a couple to find more," he says. "It is a gift, you know." After 20 years the universe finally said, 'try this one.' "

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