How Can Astrophysicists Tell Whether a Star Is Receding From or Approaching Earth?
How Tin a Star Be Older Than the Universe?
For more than 100 years, astronomers have been observing a curious star located some 190 light years away from Earth in the constellation Libra. It rapidly journeys across the sky at 800,000 mph (1.3 one thousand thousand kilometers per 60 minutes). Merely more interesting than that, Hard disk drive 140283 — or Methuselah as it'due south commonly known — is as well ane of the universe's oldest known stars.
In 2000, scientists sought to date the star using observations via the European Space Bureau'south (ESA) Hipparcos satellite, which estimated an age of sixteen billion years old. Such a figure was rather heed-blowing and also pretty baffling. As astronomer Howard Bond of Pennsylvania Land University pointed out, the historic period of the universe — adamant from observations of the cosmic microwave background — is 13.8 billion years onetime. "It was a serious discrepancy," he said.
Related: The Methuselah Star: Oldest Known Star Revealed (Gallery)
Taken at confront value, the star's predicted age raised a major problem. How could a star exist older than the universe? Or, conversely, how could the universe be younger? It was certainly clear that Methuselah — named in reference to a biblical patriarch who is said to take died anile 969, making him the longest lived of all the figures in the Bible — was old, since the metal-poor subgiant is predominantly made of hydrogen and helium and contains very little iron. It'southward composition meant the star must have come into beingness before iron became commonplace.
Simply more ii billion years older than its surround? Surely that is just not possible.
Taking a closer look at the age of Methuselah
Bond and his colleagues set themselves to the task of figuring out whether or not that initial figure of sixteen billion was authentic. They pored over 11 sets of observations that had been recorded betwixt 2003 and 2022 by the Fine Guidance Sensors of the Hubble Space Telescope, which brand a note of the positions, distances and free energy output of stars. In acquiring parallax, spectroscopy and photometry measurements, a improve sense of age could exist determined.
"1 of the uncertainties with the age of HD 140283 was the precise distance of the star," Bail told All Nearly Infinite. "It was important to go this right because we can better make up one's mind its luminosity, and from that its age — the brighter the intrinsic luminosity, the younger the star. We were looking for the parallax upshot, which meant nosotros were viewing the star six months autonomously to await for the shift in its position due to the orbital motion of the Earth, which tells united states the distance."
There were also uncertainties in the theoretical modelling of the stars, such as the exact rates of nuclear reactions in the core and the importance of elements diffusing downwards in the outer layers, he said. They worked on the thought that leftover helium diffuses deeper into the core, leaving less hydrogen to burn down via nuclear fusion. With fuel used faster, the age is lowered.
"Another factor that was important was, of all things, the corporeality of oxygen in the star," Bail said. HD 140283 had a higher than predicted oxygen-to-iron ratio and, since oxygen was not abundant in the universe for a few meg years, it pointed once more to a lower historic period for the star.
Bond and his collaborators estimated Hard disk 140283'southward age to be 14.46 billion years — a meaning reduction on the xvi billion previously claimed. That was, nonetheless, nonetheless more than than the age of the universe itself, just the scientists posed a residual uncertainty of 800 1000000 years, which Bond said made the star's age compatible with the historic period of the universe, even though information technology wasn't entirely perfect.
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"Like all measured estimates, it is bailiwick to both random and systematic error," said physicist Robert Matthews of Aston University in Birmingham, UK, who was not involved in the study. "The overlap in the error confined gives some indication of the probability of a clash with cosmological historic period determinations," Matthews said. "In other words, the best supported age of the star is in conflict with that for the derived age of the universe [as adamant past the cosmic microwave background], and the conflict can only be resolved by pushing the error bars to their extreme limits."
Farther refinements saw the age of Hard disk drive 140283 autumn a bit more. A 2014 follow-up study updated the star's age to 14.27 billion years. "The conclusion reached was that the age is about fourteen billion years and, over again, if ane includes all sources of uncertainty — both in the observational measurements and the theoretical modelling — the error is about 700 or 800 one thousand thousand years, so there is no disharmonize because 13.8 billion years lies within the star'south error bar," Bond said.
Taking a closer look at the age of the universe
For Bail, the similarities between the historic period of the universe and that of this old nearby star — both of which have been determined past different methods of assay — is "an amazing scientific accomplishment which provides very stiff evidence for the Big Bang film of the universe". He said the trouble with the age of the oldest stars is far less severe than it was in the 1990s when the stellar ages were approaching eighteen billion years or, in one case, twenty billion years. "With the uncertainties of the determinations, the ages are now like-minded," Bail said.
Yet Matthews believes the problem has non yet been resolved. Astronomers at an international conference of top cosmologists at the Kavli Institute for Theoretical Physics in Santa Barbara, California, in July 2022 were puzzling over studies that suggested different ages for the universe. They were looking at measurements of galaxies that are relatively nearby which suggest the universe is younger past hundreds of millions of years compared to the historic period determined by the cosmic microwave groundwork.
Related: 7 Surprising Things About the Universe
In fact, far from being xiii.eight billion years sometime, as estimated past the European Planck infinite telescope'southward detailed measurements of catholic radiation in 2013, the universe may be as young equally 11.4 billion years. Ane of those behind the studies is Nobel laureate Adam Riess of the Space Telescope Scientific discipline Institute in Baltimore, Maryland.
The conclusions are based on the thought of an expanding universe, as shown in 1929 by Edwin Hubble. This is cardinal to the Big Bang — the understanding that there was once a state of hot denseness that exploded out, stretching space. It indicates a starting point that should be measurable, but fresh findings are suggesting that the expansion rate is really around 10% higher than the ane suggested by Planck.
Indeed, the Planck team adamant that the expansion charge per unit was 67.4 km per second per megaparsec, simply more recent measurements taken of the expansion rate of the universe point to values of 73 or 74. That means in that location is a difference between the measurement of how fast the universe is expanding today and the predictions of how fast it should be expanding based on the physics of the early universe, Riess said. It's leading to a reassessment of accepted theories while too showing there is still much to learn about night matter and dark free energy, which are thought to be behind this conundrum.
Related: Large Bang Theory: 5 Weird Facts About Seeing the Universe'south Birth
A higher value for the Hubble Constant indicates a shorter age for the universe. A constant of 67.74 km per second per megaparsec would lead to an age of xiii.8 billion years, whereas one of 73, or even as high as 77 every bit some studies accept shown, would indicate a universe historic period no greater than 12.7 billion years. It's a mismatch that suggests, in one case again, that Hd 140283 is older than the universe. It has also since been superseded past a 2022 report published in the periodical Science that proposed a Hubble Constant of 82.4 — suggesting that the universe's age is only 11.4 billion years.
Matthews believes the answers lie in greater cosmological refinement. "I suspect that the observational cosmologists have missed something that creates this paradox, rather than the stellar astrophysicists," he said, pointing to the measurements of the stars being perhaps more than accurate. "That'southward not because the cosmologists are in any way sloppier, just considering age decision of the universe is subject to more and arguably trickier observational and theoretical uncertainties than that of stars."
So, how will scientists figure this out?
But what could exist making the universe potentially appear younger than this item star?
"There are two options, and the history of scientific discipline suggests that in such cases the reality is a mix of both," Matthews said. "In this case that would exist sources of observational error that haven't been fully understood, plus some gaps in the theory of the dynamics of the universe, such as the strength of nighttime energy, which has been the prime driver of the cosmic expansion for many billions of years now."
Related: Dark Affair and Dark Free energy: The Mystery Explained (Infographic)
He suggests the possibility that the current "age paradox" reflects time variation in dark energy, and thus a change in the rate of dispatch — a possibility theorists have found might be compatible with ideas about the fundamental nature of gravity, such as so-called causal ready theory. New research into gravitational waves could help to resolve the paradox, Matthews said.
To practise this, scientists would expect at the ripples in the material of infinite and time created by pairs of dead stars, rather than relying on the cosmic microwave groundwork or the monitoring of nearby objects such every bit Cepheid variables and supernovae to measure the Hubble Constant — the former resulting in the speed of 67 km per second per megaparsec and the latter in 73.
Trouble is, measuring gravitational waves is no like shooting fish in a barrel job, given they were just directly detected for the first fourth dimension in 2015. But according to Stephen Feeney, an astrophysicist at the Flatiron Establish in New York, a breakthrough could be made over the course of the next decade. The idea is to collect data from collisions betwixt pairs of neutron stars using the visible lite these events emit to figure out the speed they are moving relative to Earth. It also entails analyzing the resulting gravitational waves for an idea of altitude — both of which can combine to requite a measurement of the Hubble Constant that should be the most accurate yet.
The mystery of the age of HD 140283 is leading to something bigger and more than scientifically complex, altering the understanding of how the universe works.
"The most likely explanations for the paradox are some overlooked observational effect and/or something big missing from our agreement of the dynamics of the catholic expansion," Matthews said. Precisely what that "something" is, is certain to go along astronomers challenged for some time.
Additional resources:
- How Many Stars Are In The Universe?
- How Many Stars Are in the Galaxy?
- The Brightest Stars in the Sky: A Starry Inaugural
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