Archivi tag: white dwarfs

19° European Workshop on White Dwarfs

The 19th European Workshop on White Dwarfs will be held in Montréal, Canada on August 11-15th, 2014. This meeting will be marking the 40th anniversary of this series of workshops which started in Kiel, Germany, in 1974. The topics to be covered at the conference will be similar to those of the previous meetings. Continua a leggere 19° European Workshop on White Dwarfs

G191-B2B, a stellar test on a constant of nature

Un gruppo di fisici della University of New South Wales (UNSW) hanno studiato una nana bianca distante dove la gravità diventa oltre 30.000 volte maggiore rispetto alla superficie terrestre per verificare una teoria controversa sulla variabilità, o meno, di una delle costanti della natura.

Julian Berengut and his international team used the Hubble Space Telescope to measure the strength of the electromagnetic force, known as alpha, on a white dwarf star.

Berengut, of the UNSW School of Physics, said the team’s previous research on light from distant quasars suggests that alpha, known as the fine-structure constant, may vary across the Universe.

This idea that the laws of physics are different in different places in the cosmos is a huge claim, and needs to be backed up with solid evidence”, he says. “A white dwarf star was chosen for our study because it has been predicted that exotic, scalar energy fields could significant alter alpha in places where gravity is very strong. Scalar fields are forms of energy that often appear in theories of physics that seek to combine the Standard Model of particle physics with Einstein’s general theory of relativity. By measuring the value of alpha near the white dwarf and comparing it with its value here and now in the laboratory we can indirectly probe whether these alpha-changing scalar fields actually exist”. White dwarfs are very dense stars near the ends of their lives. The researchers studied the light absorbed by nickel and iron ions in the atmosphere of a white dwarf called G191-B2B. The ions are kept above the surface by the star’s strong radiation, despite the pull of its extremely strong gravitational field. “This absorption spectrum allows us to determine the value of alpha with high accuracy. We found that any difference between the value of alpha in the strong gravitational field of the white dwarf and its value on Earth must be smaller than one part in ten thousand”, Berengut says. “This means any scalar fields present in the star’s atmosphere must only weakly affect the electromagnetic force”. Berengut said that more precise measurements of the iron and nickel ions on earth are needed to complement the high-precision astronomical data. “Then we should be able to measure any change in alpha down to one part per million. That would help determine whether alpha is a true constant of Nature, or not”.

UNSW: White dwarf star throws light on constant of Nature

Physical Review Letters: Fundamental Constant Doesn’t Budge in High Gravity

arXiv: Limits on variations of the fine-structure constant with gravitational potential from white-dwarf spectra

SN 2012fr, an interesting stellar explosion case

Lo scorso anno, una serie di osservazioni relative all’esplosione di una nana bianca nei dintorni nella galassia NGC 1365 ha permesso ad un gruppo di ricercatori della Australian National University a raccogliere una grande quantità di dati su quella che essi ritengono sia una delle migliori ‘candele standard’ che viene utilizzata dagli astronomi come strumento di misura delle distanze cosmiche.

We know how a candle of a particular brightness grows fainter as it is moved further away from us. So, if we know the true brightness of the candle (in this instance, supernova SN 2012fr) and we measure its observed brightness, we can then calculate the interceding distance”, said Michael Childress. Supernova SN 2012fr left a chemical fingerprint which has been analysed by a team of researchers led by Childress from the ANU Research School of Astronomy and Astrophysics and which also includes Nobel Laureate Professor Brian Schmidt. Their data shows unprecedented, and quite unusual, layering in the material that was burnt and ejected in the explosion, especially silicon and iron. Two distinct layers of silicon were found: one thick, outer layer that had faded by the time the supernova reached its peak brightness on 12 November 2012 (16 days after the initial explosion), and one deeper layer that hardly changed for several weeks after the explosion.

As it turns out, SN 2012fr is not just another supernova but a really interesting case.

Since it was discovered within a day of explosion, we were able to study it in greater detail than almost any supernova ever discovered” Childress said. “Because we know the distance to its host galaxy (NGC 1365), this supernova actually lets us better calibrate all Type Ia Supernova observations to measure distances in the Universe, using what we call the ‘standard candle’ technique”. Despite its unusual layers, SN 2012fr appears to still be classified as a so-called ‘normal’ Type Ia Supernova, which Professor Schmidt used in his Nobel Prize winning work to discover Dark Energy, and it also presents a key link in our cosmic distance ladder. “Our analyses of SN 2012fr will increase the precision of which we can measure distances outside of our own galaxy, as well as improve our understanding of these explosive events and our ability to use them in the hunt for Dark Energy, the source of the accelerated expansion of the Universe”, said Childress.

ANU: Key link found in Cosmic Distance Ladder
arXiv: Spectroscopic Observations of SN 2012fr: A Luminous Normal Type Ia Supernova with Early High Velocity Features and Late Velocity Plateau


STARS 2013 e SMFNS 2013

The events are the second and third in a series of meetings gathering scientists working on astroparticle physics, cosmology, gravitation, nuclear physics, and related fields. As in previous years, the meeting sessions will consist of invited and contributed talks and will cover recent developments in the following topics:
STARS2013 – New phenomena and new states of matter in the Universe, general relativity, gravitation, cosmology, heavy ion collisions and the formation of the quark-gluon plasma, white dwarfs, neutron stars and pulsars, black holes, gamma-ray emission in the Universe, high energy cosmic rays, gravitational waves, dark energy and dark matter, strange matter and strange stars, antimatter in the Universe, and topics related to these.
SMFNS2013 – Strong magnetic fields in the Universe, strong magnetic fields in compact stars and in galaxies, ultra-strong magnetic fields in neutron star mergers, quark stars and magnetars, strong magnetic fields and the cosmic microwave background, and topics related to these.