Calibrating cosmic mile markers

December 11, 2018

Pasadena, CA--New work from the Carnegie Supernova Project provides the best-yet calibrations for using type Ia supernovae to measure cosmic distances, which has implications for our understanding of how fast the universe is expanding and the role dark energy may play in driving this process. Led by Carnegie astronomer Chris Burns, the team's findings are published in The Astrophysical Journal.

Type Ia supernovae are fantastically bright stellar phenomena. They are violent explosions of a white dwarf--the crystalline remnant of a star that has exhausted its nuclear fuel--which is part of a binary system with another star.

In addition to being exciting to observe in their own right, type Ia supernovae are also a vital tool that astronomers use as a kind of cosmic mile marker to infer the distances of celestial objects.

While the precise details of the explosion are still unknown, it is believed that they are triggered when the white dwarf approaches a critical mass, so the brightness of the phenomenon is predictable from the energy of the explosion. The difference between the predicted brightness and the brightness observed from Earth tells us the distance to the supernova.

Astronomers employ these precise distance measurements, along with the speed at which their host galaxies are receding, to determine the rate at which the universe is expanding. Thanks to the finite speed of light, not only can we measure how quickly the universe is expanding right now, but by looking farther and farther out into space, we see further back in time and can measure how fast the universe was expanding in the distant past. This led to the astonishing discovery in the late-1990s that the universe's expansion is currently speeding up due to the repulsive effect of a mysterious "dark" energy. Improving the distance estimates made using type Ia supernovae will help astronomers better understand the role that dark energy plays in this cosmic expansion.

"Beginning with its namesake, Edwin Hubble, Carnegie astronomers have a long history of working on the Hubble constant, including vital contributions to our understanding of the universe's expansion made by Alan Sandage and Wendy Freedman," said Observatories Director John Mulchaey.

However, the speed at which the brightness of type Ia supernova explosions fade away is not uniform. In 1993, Carnegie astronomer Mark Phillips showed that the explosions that take longer to fade away are intrinsically brighter than those that fade away quickly. This correlation, which is commonly referred to as the Phillips relation, allowed a group of astronomers in Chile, includingPhillips and Texas A&M astronomer Nicholas Suntzeff, to develop type Ia supernovae into a precise tool for measuring the expansion of the universe.

Studying the supernovae using the near-infrared part of the spectrum was crucial to this finding. The light from these explosions must travel through cosmic dust to reach our telescopes, and these fine-grained interstellar particles obscure light on the blue end of the spectrum more than they do light from the red end of the spectrum in the same manner as smoke from a forest fire makes everything appear redder. This can trick astronomers into thinking that a supernova is farther away than it is. But working in the infrared allows astronomers to peer more clearly through this dusty veil.

"One of the Carnegie Supernova Project's primary goals has been to provide a reliable, high-quality sample of supernovae and dependable methods for inferring their distances," said lead author Burns.

"The quality of this data allows us to better correct our measurements to account for the dimming effect of cosmic dust" added Mark Phillips, an astronomer at Carnegie's Las Campanas Observatory in Chile and a co-author on the paper.

The calibration of these mile markers is crucially important, because there are disagreements between different methods for determining the universe's expansion rate. The Hubble constant can independently be estimated using the glow of background radiation left over from the Big Bang. This cosmic microwave background radiation has been measured with exquisite detail by the Planck satellite, and it gives astronomers a more slowly expanding universe than when measured using type Ia supernovae.

"This discrepancy could herald new physics, but only if it's real," Burns explained. "So, we need our type Ia supernova measurements to be as accurate as possible, but also to identify and quantify all sources of error."
-end-
Other Carnegie co-authors on the paper include: Carlos Contreras, Jorge Anais, Luis Boldt, Luis Busta, Abdo Campillay, Sergio Castellon, Gaston Folatelli, Barry Madore, Consuelo Gonzalez, Wojtek Krzeminski, Nidia Morrell, Eric Persson, Miguel Roth, Francisco Salgado, Jacqueline Serón, and Simon Torres. The other co-authors are: Emilie Parent of McGill University; Maximilian Stritzinger of Arhus University; Kevin Krisciunas and Nicholas B. Suntzeff of Texas A&M University; Wendy Freedman of the University of Chicago; Eric Y. Hsiao and Peter Hoeflich of Florida State University; and Mario Hamuy of Universidad de Chile.

The Carnegie Supernova Project is supported by the U.S. National Science Foundation. Computing resources for this work were made possible by the Ahmanson Foundation. The Cynthia and George Mitchell Foundation and Sheridan Lorenz supported several CSP workshops.

The Carnegie Institution for Science (carnegiescience.edu) is a private, nonprofit organization headquartered in Washington, D.C., with six research departments throughout the U.S. Since its founding in 1902, the Carnegie Institution has been a pioneering force in basic scientific research. Carnegie scientists are leaders in plant biology, developmental biology, astronomy, materials science, global ecology, and Earth and planetary science.

Carnegie Institution for Science

Related Supernova Articles from Brightsurf:

Scientists discover supernova that outshines all others
A supernova at least twice as bright and energetic, and likely much more massive than any yet recorded has been identified by an international team of astronomers, led by the University of Birmingham.

Supernova observation first of its kind using NASA satellite
Their research, detailed in the Monthly Notices of the Royal Astronomical Society, represents the first published findings about a supernova observed using TESS, and add new insights to long-held theories about the elements left behind after a white dwarf star explodes into a supernova.

Astronomers find possible elusive star behind supernova
Astronomers may have finally found a doomed star that seemed to have avoided detection before its explosive death.

Stellar thief is the surviving companion to a supernova
Hubble found the most compelling evidence that some supernovas originate in double-star systems.

Supernova may have 'burped' before exploding
Only by increasing the rate at which telescopes monitor the sky has it been possible to catch more Fast-Evolving Luminous Transients (FELTs) and begin to understand them.

An unusual white dwarf may be a supernova leftover
Astronomers have identified a white dwarf star in our galaxy that may be the leftover remains of a recently discovered type of supernova.

Researchers show how to make your own supernova
Researchers from the University of Oxford are using the largest, most intense lasers on the planet, to for the first time, show the general public how to recreate the effects of supernovae, in a laboratory.

The big star that couldn't become a supernova
For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole.

Seeing quadruple: Four images of the same supernova, a rare find
Galaxies bend light through an effect called gravitational lensing that helps astronomers peer deeper into the cosmos.

Explosive material: The making of a supernova
Pre-supernova stars may show signs of instability for months before the big explosion

Read More: Supernova News and Supernova Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.