Methuselah star (HD 140283) is a yellow subgiant located in the constellation Libra. It is one of the oldest stars known. With an estimated age of 14.46 ± 0.8 billion years, the star appears older than the universe itself. Located at a distance of 202.4 light years from Earth, it is one of the nearest Population II stars to the Sun. With an apparent magnitude of 7.205, Methuselah is invisible to the unaided eye.
HD 140283 is a yellow subgiant star of the spectral type G0IV-V m-5. It is 2.04 times larger than the Sun and 4.82 times more luminous. The star has an estimated mass of 0.780 or 0.805 solar masses and a surface temperature of 5,787 K. It is a slow spinner, with a projected rotational velocity of up to 3.9 km/s. With a metallicity of -2.40 dex, Methuselah really earns its nickname. It is one of the most metal-poor (and therefore oldest) stars ever discovered.
The estimated age of 14.46 billion years for Methuselah was determined in a study published in 2013. At the time, Methuselah was the oldest star known. The study used the Fine Guidance Sensors of the Hubble Space Telescope and measured a trigonometric parallax of 17.15 milliarcseconds for the star and used the precise distance to determine the star’s age. Earlier estimates were even higher, giving an age of 16 billion years.
A study that used interferometric and spectroscopic measurements, as well as photometry, determined a limb-darkened diameter of 0.353 ± 0.013 milliarcseconds for Methuselah. The study derived a temperature of 5,534 K or 5,647 K and a radius of 2.21 solar radii. The same study performed bolometric flux fitting for an interstellar extinction of 0.0 and 0.1 magnitudes and derived a mass of 0.780 solar masses and an age of 13.7 ± 0.7 billion years or a mass of 0.805 solar masses and an age of 12.2 ± 0.6 billion years, depending on the degree of extinction. The study suggested that asteroseismic observations were necessary to derive the star’s mass and age with a greater degree of certainty.
Is Methuselah the oldest star?
HD 140283 is one of the oldest stars known, but there are uncertainties in its estimated age. While it currently has a higher estimated age than fellow methuselahs SMSS J031300.36−670839.3 (13.6 billion years), BD+17°3248 (13.8 ± 4 billion years), HE0107-5240 (about 13 billion years), HE 1327-2326 (age uncertain), HE 1523-0901 (13.2 billion years), HD 122563 (13 billion years), Sneden’s Star (BPS CS22892-0052, 13 billion years), Caffau’s Star (SDSS J102915+172927, 13 billion years) and Cayrel’s Star (BPS CS31082-0001, 12.5 ± 4 billion years), it is usually SMSS J031300.36−670839.3 that it cited as the oldest star with an accurately determined age.
Is Methuselah older than the universe?
Even though the estimated age of Methuselah (14.46 ± 0.8 billion years) is higher than the age of the universe (13.787 ± 0.020 billion years), the star cannot really be older because it could not have formed before the Big Bang. With a margin of error of 0.8 billion years, the star may be as young as 13.66 billion years, which does not conflict with the age of the universe. However, Methuselah must have formed shortly after the Big Bang.
A 2014 study updated the star’s age to 14.27 ± 0.38 billion years.
Even though HD 140283 is exceptionally old and made almost entirely of hydrogen and helium, it is not a Population III star since it does have some metals. Population III stars are a hypothetical group of very massive and virtually metal-free stars that formed in the early universe, only a few hundred million years after the Big Bang. Like all exceptionally massive stars, they lived very short lives before going out as supernovae. These stars have not been observed directly, but some of them may still be visible in gravitational lensing, even though they are long gone.
Methuselah is a Population II star, a metal-poor star that formed when the universe was still young. Population II stars are usually cooler and less luminous than the younger Population I stars. Even though they have low metallicity (an indicator of an older age), Population II stars typically have a higher ratio of alpha process elements (oxygen, silicon, neon, and others) relative to iron. This may be due to Type II supernovae supplying more material to the interstellar medium when these stars were formed. The heavier elements supplied by Type Ia supernovae came later.
HD 140283 is a high-velocity star whose light is blueshifted since the star is moving in our direction. Methuselah has been known to astronomers for over a century due to its high proper motion and velocity. It travels across the sky so fast that it moves by a full Moon width in only 1,500 years. The star’s fast motion across the sky indicates that Methuselah is only visiting our stellar neighbourhood at a speed of 1.3 million kilometres per hour (800,000 mph). Like other exceptionally old Population II stars, it hails from the galactic halo. Its orbit through the Milky Way plane will eventually take the star back to the Milky Way halo.
HD 140283 is believed to have formed in a dwarf galaxy that was swallowed by the Milky Way more than 12 billion years ago.
Methuselah lies in the region of the sky between Zeta Ophiuchi in the constellation Ophiuchus and Zubeneschamali, the brightest star in Libra. With an apparent magnitude of 7.205, the star requires binoculars to be seen.
HD 140283 is located in the constellation Libra. Like other zodiac constellations, Libra was first catalogued by the astronomer Ptolemy of Alexandria in his Almagest, written around 150 CE. The constellation occupies 538 square degrees of the southern sky and is the 29th largest of the 88 constellations.
Once considered part of the neighbouring Scorpius, Libra’s brightest stars are easily recognizable as they appear as the extended claws of the celestial scorpion. With only two stars brighter than magnitude 3.00, Libra is not particularly bright, but its scales asterism is visible in clear, dark skies near the claws of Scorpius.
Notable stars in Libra include the luminaries Zubeneschamali and Zubenelgenubi, the semiregular variable red giant Brachium, the yellow giant Zubenelhakrabi, and the red dwarf Gliese 581, which hosts three confirmed planets, including Gliese 581c, an Earth-like planet found to be orbiting in the star’s habitable zone.
Interesting deep sky objects in the constellation include the barred spiral galaxies NGC 5885 and NGC 5792, the active spirals NGC 5793 and NGC 5728, the unbarred lenticular galaxy NGC 5890, and the bright, large globular cluster NGC 5897.
The best time of year to observe the stars and deep sky objects in Libra is during the month of June, when the constellation climbs high above the horizon in the evening sky. Libra is visible in its entirety from locations between the latitudes 65° N and -90° S.
The 10 brightest stars in Libra are Zubeneschamali (Beta Lib, mag. 2.61), Zubenelgenubi (Alpha Lib, mag. 2.741), Brachium (Sigma Lib, mag. 3.29), Upsilon Librae (mag. 3.628), Tau Librae (mag. 3.68), Zubenelhakrabi (Gamma Lib, mag. 3.91), Theta Librae (mag. 4.136), 16 Librae (mag. 4.49), Iota1 Librae (mag. 4.54), and 37 Librae (mag. 4.61).
Methuselah star – HD 140283
|Spectral class||G0IV-V m-5|
|Apparent magnitude||7.205 ± 0.02|
|Distance||202.4 ± 0.9 light years (62.1 ± 0.3 parsecs)|
|Parallax||16.1140 ± 0.0720 mas|
|Radial velocity||-170.37 ± 0.15 km/s|
|Proper motion||RA: −1114.869 ± 0.124 mas/yr|
|Dec.: −303.574 ± 0.106 mas/yr|
|Mass||0.780 or 0.805 M☉|
|Luminosity||4.82 ± 0.27 L☉|
|Radius||2.04 ± 0.04 R☉|
|Temperature||5,787 ± 48 K|
|Metallicity||−2.40 ± 0.10 dex|
|Age||14.46 ± 0.8 billion years|
|Rotational velocity||≤ 3.9 km/s|
|Surface gravity||3.6 cgs|
|Right ascension||15h 43m 03.0967798658 s|
|Declination||−10° 56′ 00.595803430″|
|Names and designations||HD 140283, HIP 76976, SAO 159459, GJ 1195, BD−10 4149, CSV 101522, GC 21124, GCRV 9069, JP11 2636, LFT 1220, LHS 405, LTT 6279, NLTT 40989, LAL 28607, PLX 3552.00, PPM 230636, UBV 13389, TYC 5601-694-1, Gaia DR2 6268770373590148224|