In Search of Ancient Suns

HD 122563 closeup
Sixth-magnitude HD 122563 in Boötes is the brightest, oldest star seen within the night time sky. Formed practically 13 billion years in the past, it is a member of the Milky Way’s outer halo.
DSS2 / Aladin Sky Atlas

Older folks by no means run out of tales. After all, they’ve seen a couple of issues. Older stars likewise have tales to inform. They stood by throughout the Milky Way’s youth, when it eagerly devoured up smaller galaxies till lastly rising as one of the cosmic kingpins. The first planets fashioned below their watch. And whereas galactic supernovae are few and much between at this time, from the lengthy perspective of these historical suns, they pop like flash bulbs at a press convention, their stays molded and reignited into new generations of stars. Stories to inform certainly.

What defines outdated? Certainly the Sun is outdated. It emerged from the solar nebula 4.6 billion years in the past, a good age by most measures. But it does not evaluate to stars in globular clusters which have saved their wicks lit for some 12.8 billion years. While not the primary technology of stars to type within the universe, globular suns are so historical that they preceded the formation of the Milky Way galaxy as we all know it. They had been the primary clots of stars to type within the huge cloud that will ultimately collapse to type the galaxy’s bulge and finally its spiral disk. Through all of it, the globulars watched from the periphery — our galaxy’s halo — the place most of them reside to today.

Timeline of the universe
A timeline of the universe reveals when the primary stars emerged, round 180 million years, give or take, after the Big Bang. Their energetic radiation ionized the impartial hydrogen gas that then permeated the universe.
N. R. Fuller / National Science Foundation

Cosmology teaches us that the universe originated in a primeval fireball ~13.8 billion years in the past, so you possibly can’t get any older than that. Some stars come shut. The first technology of stars fashioned between 100 and 250 million years after the Big Bang from hydrogen and helium, the 2 most plentiful components produced within the formative universe. Fusion of these atomic lightweights inside their cores produced heavier components comparable to carbon, oxygen, and nitrogen, which had been expelled into space when the stars exploded as supernovae. Mixed with wholesome quantities of primordial hydrogen and helium, these new components wound up within the subsequent technology of stars.

Milky Way Galaxy structure
Our Milky Way galaxy seen from a hypothetical outsider’s viewpoint. Open star clusters and emission nebulae usually reside throughout the spiral arms, residence to younger Population I stars, whereas globular clusters and older Population II stars pepper the spherical halo surrounding the disk. Some 26,000 light-years from our solar system, the central bulge lurks behind mud clouds in Sagittarius.
Sky & Telescope with additions by the writer

Astronomers name components heavier than helium “metals,” so future generations of stars steadily grew to become enriched in metals. Measuring a star’s metallic content material, then, is a helpful way to find out its age. The fewer heavier components noticed, the older the star. Many of these metal-poor stars, dubbed Population II, inhabit the galactic halo and central bulge as a result of they preceded the formation of the Milky Way’s spiral disk, residence to younger Population I stars like our Sun. By extension, probably the most historical stars — that first technology with no metals in any respect — belong to the elusive Population III. I exploit the phrase elusive as a result of we’re nonetheless trying to find definitive proof that any nonetheless exist.

Let’s Meet These Ancient Stars

Boötes and Libra
Both HD 122563 and HD 140283 are nicely positioned for commentary on May nights. They’re shiny sufficient to simply present on this 8-second publicity at f/2.8 and ISO 2500.
Bob King

We’re going to pay a go to to 5 extraordinarily metal-poor stars which have extra in widespread with their primeval cohorts than most of the stars that spangle the sky on a darkish night time. We’ll start our pilgrimage to the traditional ones with the brightest, HD 122563, a magnitude-6.2 red large in Boötes. Located 950 light-years away within the galactic halo it is about 12.6 billion years outdated. If the Sun’s a middle-aged 45 years outdated, say, then HD 122563 could be its nice grandparent, aged 123 years. Through the telescope the star glowed pale orange and serene.

Methuselah Star
HD 140283, nicknamed the Methuselah Star, is seen in binoculars.
DSS2 / Aladin Sky Atlas

Next, we meet one other halo member that may simply be the oldest star seen in an newbie telescope. Never thoughts a telescope, binoculars will do. Dubbed the Methuselah Star, HD 140283 is a magnitude-7.2 object 202 light-years away in Libra. It belongs to the subgiant class with a mass 0.8 occasions solar however twice as large round and virtually 5 occasions as luminous. After a exact willpower of its distance utilizing the Hubble Space Telescope (HST), a 2014 study concluded that Methuselah was one of the oldest stars but found, with an age of 14.27 ± 0.38 billion years.

Star R.A. Dec. Mag. Age
HD 122563 14h 02.5m +09° 41.2′ 6.2 12.6 Ga
HD 140283 15h 43.1m –10° 56.0′ 7.2 14.5±0.8 Ga
HE 1523-0901 15h 26.0m – 09° 11.6′ 11.5 13.2 Ga
BD+17°3248 17h 28.2m +17° 30.6′ 9.3 13.8±4 Ga
Sneden’s Star 22h 17.0m –16° 39.5′ 13.2 ~13 Ga
Star ages are given in gigayears. One Ga = 1 billion years.

So wait. Is it older than the universe? Of course that may’t be. Slight uncertainties in distance and stellar modeling depart sufficient room for it to have been born post-Big Bang. But make no mistake. It’s actually, actually outdated, more likely to have fashioned from enriched materials after the metal-free technology exploded as supernovae. Despite its age, HD 140283 races throughout the galaxy at 800,000 miles per hour (1.3 million km/h) like a gold-medalist sprinter. For the second it is close to our solar system, however the galactic halo is residence candy residence.

HD 122563 and HD 140283 detailed maps
These maps plot the areas of HD 122563 in Boötes (left) and HD 140283 in Libra (proper). Stars are proven to magnitude 7 (left) and magnitude 8 (proper). North is up in all maps.

Libra hosts one other of the “old ones” in He 1523-0901, a red large embering away 2.2° due east of Beta (β) Librae and 4.5° northwest of HD 140283. It’s about 7,500 light-years from Earth and shines extra faintly at magnitude 11.5, so you may want a 4.5-inch telescope to identify it. Aged 13.2 billion years, the star was probably current on the Milky Way’s first celebration, lengthy earlier than get together hats would come into trend.

BD+17°3248 and He 1523-0901 detailed maps
On the left, stars are plotted to magnitude 10 for BD+17°3248 and magnitude 11.5 for He 1523-0901 (proper).

From right here, tilt your telescope northward to Hercules for a have a look at BD+17°3248, a magnitude-9.3 orange subgiant 13.8 ± 4 billion years outdated and roughly 2,600 light-years away.

In 2002, a crew of astronomers utilizing the HST actually discovered gold right here, the primary time the factor had ever been noticed in a star aside from the Sun. Its outer ambiance is also tainted with radioactive thorium and different heavy components. These may solely have originated by way of a course of known as rapid neutron capture that happens when huge stars explode as supernovae. Given BD+17°3248’s superior age, it could nicely have been solid from the dregs of the sought-after Population III clan.

We finish with Sneden’s Star, a faint red large barely extra huge than the Sun located 17,000 light-years from Earth within the Milky Way’s halo. Located in Aquarius, this outdated Population II star is simply now rising into the morning sky. Look for it about 5.5° south of Jupiter in early May. At magnitude 13.2 you may want an 8-inch telescope for a very good look.

Sneden's Star maps
The huge map offers context for Sneden’s Star, whereas the inset (left) is an in depth chart with stars to magnitude 13.5. The star is situated south of a small, umbrella-like asterism.

Sneden’s Star is called for Chris Sneden of the University of Texas (Austin) who, alongside along with his crew, measured the abundance of 53 components within the star. It hails from ~13 billion years in the past and like BD+17°3248 possesses heavy components fashioned by neutron seize.

The different day, whereas climbing a ridge path not removed from my residence, I encountered a small stand of outdated progress timber — behemoth white pines greater than 200 years outdated. I felt respect for the timber. They had survived thunderstorms, altering local weather, and illness to face proudly within the current. In the identical way, these historical suns proceed to shine when so many others have gone darkish. They are our eyes. Through them we see nothing lower than the start and evolution of the galaxy we name residence.


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