#hd 140283

[chibinotan]

Oldest Known Milky Way’s Star

[thenewenlightenmentage]

New Insights Into the First Stars of the Universe --"Too Faint to be Directly Observed"

The oldest known star with a well-determined age, the "Methuselah star," cataloged as HD 140283, could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma. This  ancient star has been known about for more than a century because of its fast motion across the sky.  

But the very first stars have yet to be directly observed. They are faint, although future space missions and giant telescopes hope to spot them. Meanwhile, theorists thinking about them have for several decades relied on basic physical concepts and computational simulations.

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[thenewenlightenmentage]

The Oldest Star in the Universe? --"A Primeval Dwarf Galaxy Sucked into the Emerging Milky Way"

"We have found that this is the oldest known star with a well-determined age," said Howard Bond of Pennsylvania State University and the Space Telescope Science Institute. The star could be as old as 14.5 billion years (plus or minus 0.8 billion years), which at first glance would make it older than the universe's calculated age of about 13.8 billion years, an obvious dilemma. But earlier estimates from observations dating back to 2000 placed the star as old as 16 billion years, an age range that presented a potential dilemma for cosmologists.

This Methuselah star has seen many changes over its long life. It was likely born in a primeval dwarf galaxy. The dwarf galaxy eventually was gravitationally shredded and sucked in by the emerging Milky Way over 12 billion years ago. The star retains its elongated orbit from that cannibalism event. Therefore, it's just passing through the solar neighborhood at a rocket-like speed of 800,000 miles per hour.

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[thenewenlightenmentage]

Nearby Ancient Star is Almost as Old as the Universe

A metal-poor star located merely 190 light-years from the Sun is 14.46+-0.80 billion years old, which implies that the star is nearly as old as the Universe!  Those results emerged from a new study led by Howard Bond.  Such metal-poor stars are (super) important to astronomers because they set an independent lower limit for the age of the Universe, which can be used to corroborate age estimates inferred by other means.

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[bluestockingvanguard]

The Lives and Times of Very Ancient Stars

There’s recently been a lot of hullabaloo about what may be the oldest star ever discovered.  Official name HD 140283, this second-generation star is thought to be at least 13.2 billion years old.  (For comparison, the universe is presently thought to be ~13.8 billion years old.)  “Second generation” means exactly that- the first stars following the Big Bang coalesced and died, most of them in supernovae due to their extraordinary size, and second generation stars formed from their remains.  Though the article recently published in Nature magazine did not specify stellar mass, this ancient star must be very small to have husbanded its nuclear fuel for so very long.

Many articles have been published on this topic since the discovery was announced January 10.  However, I see many of the same scientific questions arising in the commentary of these articles.  I’d like to take some time to address the most common of these as they raise basic questions of stellar mechanics and evolution that are required for understanding many topics in astronomy.

The article reports HD 140283 contains traces of heavier elements that identify it as a second generation star.  Shouldn’t the abundance be higher after all those years of fusion?

Stellar fusion is a much more complicated process than it’s made out to be.  The key point for our very old star is that it is likely to still be on the main sequence (stars still fusing hydrogen in to helium).  I was unable to find sources confirming its stage of evolution, but given that it must be a red dwarf (a class of very low-mass stars) this seems probable.  Not enough time has passed for the star to exhaust its hydrogen fuel, as the lower the mass the slower the star burns.  The star has simply not advanced far enough to begin to fuse heavier elements.  It’s also important to note that in astronomy, “heavy elements” can refer to anything heavier than hydrogen and helium, since those elements dominate the universe and are primordial, having been created in quantity during the cooling of the early universe.

Some heavy elements are only created via special processes rather than fusion reactions.  All elements heavier iron were first created by supernovae.  (Once they existed, it became possible to generate elements via something called the s-process, using the heavy elements as seeds, but that’s another topic.)  We know HD 140283 must be a second-generation star because it contains elements that simply did not exist in the universe when the first generation of stars formed, and it has them in the right abundance for the second generation.  The universe is becoming increasingly enriched in heavy elements as time goes on.

The distance to HD 140283 is estimated at 190 light years, relatively close to the Sun in astronomical terms.  How is it possible the oldest star is within striking distance, or that two stars of such different age could exist in close proximity?

First of all, nobody is claiming HD 140283 is the “oldest” star, though I’ve seen this assumption made repeatedly.  It’s simply the oldest we’ve detected to date (probably). 

The Sun’s age is estimated at only 4.6 billion years.  It coalesced well after galaxies were firmly established in our universe.  HD 140283, however, first began to shine while galaxies were still forming.  It’s “allegiance”, as it were, may not be as solid as our sun’s.  Rather than forming within the Milky Way, it may have simply found itself in the large gravitational hole that became our galaxy.  Or it could have been one of its very first stars.

Stars tend to form in “nurseries” known as giant molecular clouds, enormous nebulae of gas and dust, often staying together as a loosely bound group after formation.  These groups are known as open clusters and can contain up to a few thousand stars that possess similar age and chemical composition.  However, open clusters are easily disrupted by close encounters with other gravitational bodies, and over the course of 13 billion years, it’s not surprising that some of those early stars may be wandering alone.  Additionally, some stars are interlopers in our galaxy, having been ejected from satellite galaxies, globular clusters orbiting the Milky Way, or even more exotic locales.  Information about the orbit and velocity of HD 140283 could tell us much about its possible origins.

Finding this ancient star in our backyard isn’t so much of a stretch as a happy coincidence, and not as statistically unlikely as it first sounds.

[thenewenlightenmentage]

Astronomers have discovered a Methuselah of stars — a denizen of the Solar System's neighbourhood that is at least 13.2 billion years old and formed shortly after the Big Bang.

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