Two supernovasS in a galaxy, and a galaxy so far away that we see it as it was 10 billion years ago, could be crucial in helping to reveal the expansion rate of the universe. This is a measurement that has caused some tension within the scientific community.
The galaxy and the two supernovae were imaged by the Hubble and James Webb space telescopes. The galaxies are made visible by the power of gravitational lens – a phenomenon in which large amounts of mass, such as that in a cluster of galaxies, can deform room into a “lens” shape that can then magnify and distort the light from more distant galaxies.
In 2016, the Hubble Space Telescope imaged the galaxy MRG-M0138, but the images were not fully analyzed until three years later. The light from MRG-M0138 is distorted into five separate images by the lens of the galaxy cluster MACS J0138.0-2155, which is 4 billion light years away from us. The images don’t exactly look like galaxies we know, because they are distorted into arcs due to the imperfect lens situation.
Related: The ‘Einstein ring’ captured by the James Webb Space Telescope is the most distant object ever seen through gravitational lensing
However, while studying the Hubble images in 2019, astronomers noticed the bright light from a supernova in MRG-M0138. A type Ia supernova is the explosion of a white dwarfeither by a collision with another white dwarf, or by steal enough matter of a close companion.
But now astronomers are observing MRG-M0138 with the James Webb Space Telescope (JWST) have discovered one second type Ia supernova in the distant galaxy.
The first supernova was nicknamed ‘Requiem’; this second supernova is called “Encore”. MRG-M0138 is the furthest galaxy we can see with two Type Ia supernovae, and that’s actually very important in helping to solve what may be the world’s biggest puzzle. cosmology straight away.
When astronomers measure the expansion rate of the universe – a quantity we call the Hubble constant — they are given two incompatible values. Although at first glance there appears to be no error in either measurement, they obviously cannot both be correct. So there is either an undetected error in our measurements, or there is exotic new physics involved.
One way to measure the Hubble constant is by analyzing Hubble’s constant cosmic microwave background (CMB) radiation left behind by the Big bang. The CMB is spotted by small temperature differences that correspond to variations in the density of the primordial matter that grew into the galaxies and clusters of galaxies we see today. We see these variations and large-scale structures there the universe today are directly related, and based on what we know about the standard model from cosmology, astronomers can use this relationship to derive a value of the Hubble constant equal to 67.4 kilometers (41.9 miles) per second per megaparsec. (A megaparsec is 3.26 million light years, so what this means is that every second a certain volume of space with a diameter of 3.26 million light years expands by 67.4 kilometers.)
However, Type Ia supernovae are also useful for measuring cosmic distances – and Hubble’s constant. That’s because they have a standardizable maximum Brightness from which we can judge their true intrinsic clarity. Then, based on how bright or faint they appear to us, we can calculate how far away they must be. From there, astronomers can compare this distance to that of the supernovae redshift, which is a measure of how quickly space is expanding, thereby expanding the wavelengths of light coming from the supernova – to obtain the Hubble constant. The final calculation is done using the Hubble-Lemaître law, which says that the recession rate is equal to the distance multiplied by Hubble’s constant. Using this method, astronomers calculate 73.2 kilometers (45.5 miles) per second per megaparsec, which is greater than the CMB-derived value.
However, the lensed supernovae in MRG-M0138 have an added benefit: they will appear in five different lensed views of the galaxy.
‘When a supernova explodes behind a gravitational lens, its light reaches out Soil through different pathways,” said Justin Pierel of the Space Telescope Science Institute and Andrew Newman of the Observatories of the Carnegie Institution for Science in a joint meeting. rack.
These paths have different lengths, so the supernova can appear in the images separated by days, weeks or even years.
“By measuring differences in the times at which the supernova images appear, we can measure the history of the universe’s expansion rate, known as Hubble’s constant, which is a major challenge in cosmology today,” Pierel and Newman said.
Lensed supernovae are rarely found; fewer than a dozen are known. This makes the two Type Ia supernovae in MRG-M0138 exceptionally valuable.
Related stories:
— Why do some images from the James Webb Space Telescope show warped and repeating galaxies?
— The Sun’s gravitational lens could help find life on exoplanets
— Gravitational waves can help us figure out how quickly the expansion of the universe is accelerating
However, there is a catch. Although most images of the two supernovae have emerged, one of the light paths is predicted to be much longer, based on models of the distribution of dark matter in the lens cluster. These final images are not expected to appear until the mid to late 2030s.
“Supernovae are normally unpredictable, but in this case we know when and where to look to see the final performances of Requiem and Encore,” said Pierel and Newman. “Infrared observations around 2035 will produce their last hurray, providing a new and accurate measurement of the Hubble constant.”
While the aging Hubble Space Telescope may no longer be active in 2035, the JWST hopefully still will be. If so, and if it can detect the appearance of the final images of Requiem and Encore, the measurement of the Hubble constant they provide could help resolve the question of whether the so-called Hubble tension is just an experimental error or a real phenomenon.