Supernova whose light will ‘reappear’ in 60 years could solve the biggest problem in cosmology
Two incredibly rare supernovas that erupted billions of years ago offer a unique opportunity to explain cosmology’s greatest mystery: how fast is the universe expanding?
But there’s a problem: even though astronomers have already observed these exploding stars, it will take up to 60 years for their light to reach us again.
A phenomenon called gravitational lensing has split the light from these obliterated stars into multiple images, each of which travels a different path through space-time to reach us. As a result, researchers will one day be able to measure the time delay between these ghostly images to provide an unprecedented constraint on the rate of expansion of the universe – a problem that has long plagued scientists, because the universe appears to expand at different rates depending on where they look.
Cosmic magnifying glasses reveal the invisible
These supernova observations are among the first results from the Vast Exploration for Nascent, Unexplored Sources (VENUS) cash program. The VENUS survey uses the James Webb Space Telescope (JWST) to observe 60 dense galaxy clusters, which act as cosmic lenses that split and focus light from extremely distant, otherwise invisible sources, such as supernovas.
This cosmic phenomenon, called gravitational lensing, is a direct consequence of the effect of gravity on the atmosphere. fabric of space-time and was first proposed by Albert Einstein in his theory of relativity. This occurs when a massive celestial object, such as a galaxy cluster, bend the light coming from a more distant source located behind it, thus magnifying the object.
“Strong gravitational lensing turns galaxy clusters into nature’s most powerful telescopes,” Seiji Fujimotoprincipal investigator of the VENUS program and astrophysicist at the University of Toronto, said in a statement statement. “VENUS was designed to detect the rarest events in the distant Universe as much as possible, and these were targeted [supernovas] are exactly the kind of phenomena that only this approach can reveal. »
SN Ares is the first lensed supernova discovered via the VENUS program. The explosion occurred nearly 10 billion years ago, when the universe was about a third of its current age. The warping of space-time caused by a foreground galaxy cluster, MJ0308, split the light from SN Ares into three images.
An image has already reached our telescopes. But the light from the other two images passes much closer to the massive center of MJ0308, so it experiences a much greater slowdown due to gravitational time dilation. Therefore, the other two SN Ares images will arrive in about 60 years – an unprecedented delay.
“Such a long delay between images of a strong lensing supernova has never been observed before and could provide an opportunity for a predictive experiment that could place incredibly precise constraints on cosmological evolution,” Larison said in a statement. statement.
Meanwhile, a delayed image of SN Athena, which went supernova when the universe was about half its current age, is expected to arrive within the next two years. Although she won’t be as cosmologically accurate as her mythological half-brother Ares, Athena will reveal just how precise our predictive powers have become.
A badly needed natural experiment
The predicted reappearance of these supernovas, compared to their actual arrival times in the future, will provide precise constraints on the rate of expansion of the universe, a value known as Hubble constant.
Interestingly, when cosmologists measure the Hubble constant, they get different values based on the method of measurement – a disparity known as Hubble voltage. Calculations based on the cosmic microwave background – the oldest light in the universe, emitted when the cosmos was only 380,000 years old – give a universal expansion rate of 67 kilometers per second per megaparsec.
However, calculations based on observations from the Hubble Space Telescope pulsating cepheid starsused as “standard candles” for their specific luminosity models, give a value of 73 kilometers per second per megaparsec.
In the observable sphere of the cosmos, delayed images from SN Ares and SN Athena could help reconcile the Hubble tension.
“If we can measure the difference between when these images arrive, we get back a measure of the physical scale of the lensing system that spans the Universe between the supernova and us here on Earth,” Larison told Live Science via email. “Any distance measurement that we can make in the Universe in this way tells us how the Universe has evolved over cosmic time, because these distances directly depend on this evolution.”
Just as importantly, lensed supernovas allow astronomers to make this measurement in a “single, coherent step,” Larison added.
The time frames of these supernovas also allow an independent measurement method – unrelated to the cosmic microwave background or standard candles like Cepheid stars – at a time when such measurement is “cruelly needed” to test “a possible unknown systematics” governing cosmological expansion.
From the Big Bang to the great mystery
Coincidentally, 60 years have passed since the first formal suggestion of using lensed supernovas as a tool to explore the expansion of the universe. However, less than 10 of these supernovas had been discovered before the VENUS program observations.
“Since VENUS launched last July, we have discovered 8 new lensed supernovae in 43 observations, nearly doubling the known sample in a remarkably rapid time frame,” Larison told Live Science. “It appears that while lensed supernovae are certainly rare, the real limitation lies in observational capabilities. It is really only with JWST that we achieve the depth and wavelength coverage needed to find them en masse, which is what VENUS was designed to do.
As a result, lensing supernovas could represent one of the most exciting prospects in long-range cosmology, the study of how the universe has changed over its 13.8 billion years of existence.
The answer is pending; there is no guarantee that the expansion of the universe will continue to accelerate, especially since dark energy can weaken. If so, the current expansion of the cosmos could one day turn into contraction, which would have profound consequences for the ultimate fate of the universe.
Ultimately, SN Ares and SN Athena could hint at the potential death of the universe and whether it ends with a roar or a groan, will the cosmos collapse in a Big Crunch, or will it expand indefinitely into the thin, cold darkness of a Big Freeze?
