Carnegie Astronomers Discover New Kind of Supernova; Type Iax

This artist's conception shows the suspected progenitor of a new kind of supernova called Type Iax. 

Material from a hot, blue helium star at right is funneling toward a carbon/oxygen white dwarf star at left, which is embedded in an accretion disk. In many cases the white dwarf survives the subsequent explosion. 

Credit: Image is provided courtesy of Christine Pulliam (CfA)

Supernovae were always thought to occur in two main varieties but a team of astronomers including Carnegie's Wendy Freedman, Mark Phillips and Eric Persson is reporting the discovery of a new type of supernova called Type Iax.

This research has been accepted for publication in The Astrophysical Journal.

Previously, supernovae were divided into either core-collapse or Type Ia categories. Core-collapse supernovae are the explosion of a star about 10 to 100 times as massive as our sun. Type Ia supernovae are the complete disruption of a tiny white dwarf.

Wendy Freedman

This new type, Iax, is fainter and less energetic than Type Ia. Although both types come from exploding white dwarfs, Type Iax supernovas may not completely destroy the white dwarf.

Ryan Foley

"A Type Iax supernova is essentially a mini supernova," says lead author Ryan Foley, Clay Fellow at the Harvard-Smithsonian Center for Astrophysics (CfA). "It's the runt of the supernova litter."

The research team, which also included Max Stritzinger identified 25 examples of the new type of supernova.

Max Stritzinger

None of them appeared in elliptical galaxies, which are filled with old stars. This suggests that Type Iax supernovas come from young star systems.

Based on a variety of observational data, the team concluded that a Type Iax supernova comes from a binary star system containing a white dwarf and a companion star that has lost its outer hydrogen, leaving it helium dominated. The white dwarf collects helium from the normal star.

Researchers aren't sure what triggers a Type Iax. It's possible that the outer helium layer ignites first, sending a shock wave into the white dwarf.

Alternatively, the white dwarf might ignite first due to the influence of the overlying helium shell.

Either way, it appears that in many cases the white dwarf survives the explosion, unlike in a Type Ia supernova where the white dwarf is completely destroyed.

Mark Phillips

The team calculates that Type Iax supernovae are about a third as common as Type Ia supernovae. The reason so few have been detected is that the faintest are only one-hundredth as bright as a Type Ia supernova.

"The closer we look, the more ways we find for stars to explode," Mark Phillips said.

The Large Synoptic Survey Telescope could discover thousands of Type Iax supernovas over its lifetime.

Reference
Type Iax Supernovae: A New Class of Stellar Explosion. The Astrophysical Journal, 2013; 767 (1): 57 DOI: 10.1088/0004-637X/767/1/57

ESO Astronomers discover extremely rare triple quasar

An infrared image of the triple quasar system QQQ J1519+0627, made using the 3.5-m aperture telescope of the Calar Alto Observatory. 

The three quasars are labelled A, B and C.

Image Credit: Emanuele Paolo Farina

For only the second time in history, a team of scientists including Michele Fumagalli from the Carnegie Institution for Science in the United States have discovered an extremely rare triple quasar system.

Their work is published in the Oxford University Press journal Monthly Notices of the Royal Astronomical Society.

Quasars are extremely bright and powerful sources of energy that sit in the centre of a galaxy, surrounding a black hole.

In systems with multiple quasars, the bodies are held together by gravity and are believed to be the product of galaxies colliding.

It is very difficult to observe triplet quasar systems, because of observational limits that prevent researchers from differentiating multiple nearby bodies from one another at astronomical distances. Moreover, such phenomena are presumed to be very rare.

The team led by Emanuele Farina of the University of Insubria in Como, Italy, combined observations from the New Technology Telescope of the European Southern Observatory (ESO) at La Silla, Chile and from the Calar Alto Observatory in Spain with advanced modelling.

This enabled them to find the triplet quasar, called QQQ J1519+0627. The light from the three quasars has travelled 9 billion light years to reach us, which means the light was emitted when the universe was only a third of its current age.

Advanced analysis confirmed that what the team found was indeed three distinct sources of quasar energy and that the phenomenon is extremely rare.

Two members of the triplet are closer to each other than the third. This means that the system could have been formed by interaction between the two adjacent quasars, but was probably not triggered by interaction with the more-distant third quasar.

Furthermore, no evidence was seen of any ultra-luminous infrared galaxies (galaxies with very strong emission in infrared light), which is where quasars are commonly found.

As a result, the team proposes that this triplet quasar system is part of some larger structure that is still undergoing formation.

"Honing our observational and modelling skills and finding this rare phenomenon will help us understand how cosmic structures assemble in our universe and the basic processes by which massive galaxies form," Fumagalli said.

"Further study will help us figure out exactly how these quasars came to be and how rare their formation is," Farina added.

The above story is reprinted from materials provided by Royal Astronomical Society (RAS).