The remnant of Tycho’s supernova as seen in X-rays, showing the expanding shock wave
Image credit: X-ray: NASA/CXC/Rutgers/K.Eriksen et al.; Optical: DSS
Artist’s conception of a white dwarf slowly accreting matter from a companion star
Image credit: David A. Hardy & PPARC
Artist’s conception of a binary white dwarf system.
Image credit: Tod Strohmayer (GSFC), CXC, NASA, Illustration: Dana Berry (CXC)
An international team of scientists from the Monash University
(Melbourne, Australia), the Towson and Pittsburgh Universities (USA) and
the Max Planck Institute for Astrophysics, has shed new light on the
origins of the famous Tycho’s supernova. The research, published in Nature Astronomy,
debunks the common view that Tycho’s supernova originated from a white
dwarf, which had been slowly accreting matter from its companion in a
binary system.
Type Ia supernovae (SNe Ia) serve as standard candles of modern
observational cosmology; they also play a vital role in galactic
chemical evolution. However, the origin of these gigantic cosmic
explosions remains uncertain. Although there is a nearly universal
consensus that SNe Ia are a result of the thermonuclear disruption of a
white dwarf consisting of carbon and oxygen reaching the Chandrasekhar
mass limit (about 1.4 times the mass of our Sun), the exact nature of
their progenitors is still unknown. The white dwarf could have been
gradually accumulating matter from a companion star thus reaching the
Chandrasekhar mass limit, at which point the nuclear runaway began; or
the nuclear explosion could have been triggered by the merger of two
white dwarfs in a compact binary system. These two scenarios differ
dramatically in the level of electromagnetic emission expected from the
progenitor during millions of years prior to the explosion.
A white dwarf that is accreting material from the donor star becomes a
source of copious X-ray and extreme UV photons – the canonical accretion
scenario implies a hot and luminous progenitor that would ionize all
surrounding gas within a radius of ~10–100 parsecs (up to about 300
light-years), the so called Strömgren sphere. After the white dwarf is
disrupted in the supernova explosion, the source of ionizing emission
disappears. However, it takes quite a long time for the interstellar gas
to recombine and to become neutral again – an ionized nebula will
continue to exist around the supernova for about 100,000 years after the
explosion. Thus, the detection of even small amounts of neutral gas in
the vicinity of a supernova can help scientists to place tight
constraints on the temperature and luminoisty of the progenitor.
445 years ago, Tycho Brahe observed a stella nova (“new star”)
in the night sky. Brighter than Venus when it first appeared, it faded
over the following year. Today, we know that Tycho had observed a
nuclear disruption of a white dwarf – a type Ia supernova. Due to its
history and relative proximity to Earth, Tycho’s supernova is one of the
most well-documented examples of a Type Ia supernova.
In particular, we know from optical observations that the supernova
remnant today is expanding into the mostly neutral gas. Thus, using the
remnant itself as a probe of its environment, scientists could exclude
hot luminous progenitors that would have produced a Strömgren sphere
larger than the radius of the present remnant (~3 parsecs). This
conclusively rules out steadily nuclear-burning white dwarfs (supersoft
X-ray sources), as well as disk emission from a Chandrasekhar-mass white
dwarf accreting more than one solar mass in approximately 100 million
years (recurrent novae). The lack of a surrounding Strömgren sphere is
consistent with the merger of a double white dwarf binary, although
other more exotic scenarios may be also possible.
Contact
Gilfanov, Marat
Scientific Staff
Phone: 2227
Email: mgilfanov@mpa-garching.mpg.de
Hämmerle, Hannelore
Press officer
Phone: 3980
Email: hanne@mpa-garching.mpg.de
Original publication
1. Tyrone Woods, Parvis Ghavamian, Carlos Badenes & Marat Gilfanov No hot and luminous progenitor for Tycho’s supernova
Nature Astronomy (2017), Published online: 25 September 2017
Source / DOI
Contact
Gilfanov, Marat
Scientific Staff
Phone: 2227
Email: mgilfanov@mpa-garching.mpg.de
Hämmerle, Hannelore
Press officer
Phone: 3980
Email: hanne@mpa-garching.mpg.de
Original publication
1. Tyrone Woods, Parvis Ghavamian, Carlos Badenes & Marat Gilfanov No hot and luminous progenitor for Tycho’s supernova
Nature Astronomy (2017), Published online: 25 September 2017
Source / DOI
