Category Archives: stars

astronomy, astronomy news, starbirth, stardust, stars

Diamonds Loose in the Sky

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All that Glitters

When you look at the night sky, of course you see stars glittering up there. And, planets.  And, if you  have a telescope, you can make out the blurry wisps of nebulae and galaxies.  Nebulae are clouds of gas and dust that float in space. They can be starbirth regions, the outpouring of a star (or stars) dying, and a mixture of both.

As it turns out, when you look at the clouds of gas and dust (called circumstellar disks) surrounding some special types of stars, you are looking at something else that glitters: diamonds.  In these regions, there are countless numbers of these tiny sparklers (and I do mean tiny — most are not even the width of a human hair) swarming around in those disks. Yet around some stars, there are enough diamond specks that if you packed them all together, they’d have enough mass to make a tiny moonlet.

https://i0.wp.com/www.naoj.org/Pressrelease/2009/04/14/goto_illust_e.jpg?resize=395%2C296
Artist's conception of where diamonds are found in circumstellar disks with special conditions that lead to the formation of such diamonds. Courtesy Subaru Telescope, NAOJ. (Click to embiggen.)

How can diamonds form in space? It’s a detective story, really, and a group of scientists from Japan, Germany, and Denmark used Subaru telescope on Mauna Kea in Hawai’i, to study ayoung star called Elias 1 to solve the central riddle of that story: how can diamonds form in space?

When scientists look for diamonds in space, they are like detectives using fingerprints to trace a missing person or find the perpetrator of a crime. The fingerprints of diamond crystals take the form of  lines in the infrared wavelength of light, outside the range of visible light. The first such signature was discovered in 1983 in the circumstellar disk of Elias 1, a young star located in the direction of Taurus. It is is one of many Herbig Ae/Be (HAEBE) stars?young, very bright stars that are about 1.5-10 times as massive as our Sun.

The research team began with clues from previous laboratory research into how diamonds are formed (carbon materials are subjected to  great temperatures and pressures).  They coupled this with observations of stars that are surrounded by dust, and have partner stars that emit tremendous bursts of hard x-ray emissions.   X-rays are emitted under extremely energetic and hot conditions, so that supplies the necessary energy and pressure for a natural diamond factory in space.

The scientists knew from their research that diamonds are formed close to the stars where they exist. They aren’t floating in from random points in space.  Also, diamond stars must have special ingredients: that disk full of carbon material, a hot central star and a companion emitting hard x-rays. The star must be of intermediate mass that can warm up the disk to a medium temperature. Then, carbon onions can form, providing the cradle for diamond creation. The need for such special conditions would explain why we see so few stars with diamond signatures in their disks.

The findings of this research (more details here) will raise even more questions and speculation about the formation of these fascinating crystals. It’s possible that there are tons of diamonds that astronomers cannot yet see because their emissions are hidden from view by shells of material surrounding the stars where they exist.

binary stars, blue stragglers, stars, stellar ages, stellar classification, stellar evolution

Blue Stragglers Explained

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Stellar Cannibalism the Mechanism that Creates Them

The core of globular cluster 47 Tucanae is home to many blue stragglers, rejuvenated stars that glow with the blue light of young stars. Courtesy NASA/STScI.
The core of globular cluster 47 Tucanae is home to many blue stragglers, rejuvenated stars that glow with the blue light of young stars. Courtesy NASA/STScI.

The astronomy zoo abounds with exotic-sounding creatures like magnetars and pulsars and brown dwarfs and hot Jupiters and other intriguingly named objects.  Today, astronomers are talking about another such denizen of the zoo–the blue straggler. These are massive stars that are found in globular clusters. These “overweight” objects have been seen throughout the universe and are stars that should have died a long time ago.

Theory says that most stars in a globular are formed around the same time and should die about the same time. Yet, these big, bloated bad boys hang on and on long after their crêche-mates have exploded and died.

So, what gives with these guys?

Researchers using data taken using Hubble Space Telescope have looked at blue stragglers in a number of clusters. They discovered that these mysterious overweight stars are actually the result of “stellar cannibalism.” Essentially, they keep living by eating up the plasma from nearby stars.  The result is a massive, unusually hot star that appears younger than it is (i.e. blue and hot).

Now, you need a binary star (two stars orbiting a common center of mass) to form a blue straggler for this process to work, and when scientists looked at the mechanics of how one star in a binary can gobble up its companion’s mass, it was the key that helped resolve the mystery of how blue stragglers come into existence.

How did the astronomers figure this out?

Two researchers from Canada — Dr. Christian Knigge  of Southampton University and Professor Alison Stills of McMaster University (both in Canada) looked at blue stragglers in 56 globular clusters to figure out how these stars –which astronomers have known about for 55 years — could form.

Sills pointed out that,  “Over time two main theories have emerged: that blue stragglers were created through collisions with other stars; or that one star in a binary system was “reborn” by pulling matter off its companion. “

In the course of looking at a collection of blue stragglers, the two researchers found that the total number of of these stars in a given cluster did not correlate with a predicted collision rate, which blew away a ­ theory that blue stragglers are created through collisions with other stars.

They did, however, discover a connection between the total mass contained in the core of a globular cluster and the number of blue stragglers observed within it. Since clusters with more massive cores also contain more binary stars, the astronomers were able to infer a relationship between blue stragglers and binaries in globular clusters. Preliminary observations directly measured the abundance of binary stars in cluster cores — and what they found supported the relationship.  All of this points to “stellar cannibalism” as the primary mechanism for blue straggler formation.

Knigge commented that the only thing that made sense for the creation of blue stragglers was that at least two stars had to be involved in the creation of every blue straggler.  That makes sense, since isolated stars that contained as much mass as typical blue stragglers do could not exist in clusters. “This is the strongest and most direct evidence to date that most blue stragglers, even those found in the cluster cores, are the offspring of two binary stars,” he said.

The two scientists are still intrigued by the mechanism for blue straggler formation and want to nail down the exact details. “We will want to determine whether the binary parents of blue stragglers evolve

mostly in isolation, or whether dynamical encounters with other stars in the clusters are required somewhere along the line in order to explain our results,” Knigge said.

If you’d like more details about the detailed analysis of blue stragglers in globulars, check out the 15 January edition of Nature Magazine (if you don’t have a subscription, check out your library for it).