Scientists have assembled a large database of observations of Type Ia supernovae. It turns out that these rare explosions that are produced by white dwarfs in double systems are more diverse than previously thought. And that’s a big deal, given that researchers use them to estimate the rate of expansion of the Universe.
Research on Type Ia supernovae
A unique dataset of Type Ia supernovae being published today could change the way cosmologists measure the expansion history of the Universe. This is announced by Mathew Smith and Georgios Dimitriadis of Lancaster University, they are members of the Zwicky Transient Facility (ZTF) project, a stellar sky survey done with a new camera attached to the Samuel Oschin at Palomar Observatory in California. The work was published in the journal Astronomy & Astrophysics.
Type Ia supernovae are dramatic explosions of white dwarf stars at the end of their lives. Cosmologists use them to study distances in the Universe by comparing their fluxes as subsequent objects appear dimmer.
Lancaster astrophysicist Dr. Smith, co-director of the ZTF SN Ia DR2 release, said: “This release provides a game-changing dataset for supernova cosmology. It opens the door to new discoveries about both the expansion of the universe and the fundamental physics of supernovae.”
A new dataset on supernovae
This is the first time astrophysicists have had access to such a large and homogeneous data set. Type Ia supernovae are rare, happening about once every thousand years in a typical galaxy, but the depth and observing strategy of the ZTF allows researchers to detect nearly four supernovae per night. In two and a half years alone, the ZTF has doubled the number of Type Ia supernovae obtained over the past 30 years available for cosmology to nearly three thousand.
ZTF cosmology working group leader Dr. Mickael Rigault of the Lyon Institute of Two Infinities (CNRS) said: “For the past five years, a group of thirty experts from around the world have collected, compiled, assembled, and analyzed these data. We are now releasing it to the entire community. This sample is so unique in terms of size and homogeneity, that we expect it to significantly impact the field of supernovae cosmology and to lead to many additional new discoveries in addition to results we have already published.”
The ZTF camera, mounted on the 48-inch Schmidt Telescope at Palomar Observatory, scans the entire northern sky every day in three optical bands, reaching a depth of 20.5 star magnitudes – a million times fainter than the dimmest stars visible to the naked eye. This sensitivity allows ZTF to detect almost all supernovae within 1.5 billion light-years of Earth.
Supernovae and the accelerated expansion of the Universe
The acceleration of the expansion of the Universe, honored with a Nobel Prize in 2011, was discovered in the late 1990s with about a hundred of these supernovae. Since then, cosmologists have been investigating the cause of this acceleration caused by dark energy, which plays the role of an anti-gravitational force in the Universe.
Study co-author Professor Ariel Goobar, director of the Oskar Klein Center in Stockholm, one of the founding institutions of the ZTF, and a member of the team that discovered the accelerated expansion of the universe in 1998, said: “Ultimately, the aim is to address one of our time’s biggest questions in fundamental physics and cosmology, namely what is most of the universe made of? For that we need the ZTF supernova data.”
One of the key findings of these studies is that Type Ia supernovae inherently vary with their environment more than previously expected, and that the correction mechanism considered so far should be reviewed. This could change how we measure the expansion history of the Universe, and could have important implications for the current bias seen in the standard model of cosmology.
With this large and homogeneous dataset, scientists will be able to study Type Ia supernovae with an unprecedented level of precision and accuracy. This is a crucial step toward honing the use of Type Ia supernovae in cosmology and assessing if current deviations in cosmology are due to new fundamental physics or unknown problems in the way we derive distances.
According to phys.org
