NEWBORN PULSARS WITH A HIDDEN MAGNETIC FIELD

Image: Crab nebula as seen by Chandra. Credit: NASA/CXC/SAO/F. Seward et al.

In the center of several supernova remnants there are pulsars with significantly lower values of the dipolar magnetic field than the average radio-pulsar population (10^{12}G). A possible explanation requires the slow rotation of the proto-neutron star at birth, which is unable to amplify its magnetic field to typical pulsar levels.

However, recent studies have shown that, even in the absence of rapid rotation, magnetic fields in pulsars can be amplified by other mechanisms such as convection and the standing accretion shock instability.
An alternative possibility, the hidden magnetic field scenario, considers the accretion of the fallback of the supernova debris onto the neutron star as responsible for the submergence (or screening) of the field and its apparently low value. A high accretion rate can compress the magnetic field of the NS which can eventually be buried into the neutron star crust. As a result, the value of the external magnetic field would be significantly lower than the internal 'hidden' magnetic field.

Credit: Torres-Forné et al. 2016

Once the accretion process stops, the magnetic field might eventually reemerge.
The main conclusion of a recent paper (Torres-Forné et al. 2016) is that typical magnetic fields of a few times 10^{12}G can be buried by accreting only 0.001-0.01 solar masses, a relatively modest amount of mass. The field would only reemerge after a few thousand years.
On the contrary, magnetar-like field strengths are much harder to screen and the required accreted mass is very large, in some cases so large that the neutron star would collapse to a black hole. The anomalously weak magnetic fields should be common in very young neutron stars.

Read more>>
http://arxiv.org/pdf/1511.03823v2.pdf
http://mnras.oxfordjournals.org/content/456/4/3813.abstract

Comments

CONTAMINATION BY SUPERNOVAE IN GLOBULAR CLUSTERS

Credit: ALMA (ESO/NAOJ/NRAO)/Alexandra Angelich (NRAO/AUI/NSF) Only a small amount of the supernovae products remains trapped within globular clusters and this "catch" only occurs in the most massive cases (mass cluster ≥ 10^6 solar masses).

Forest of Molecular Signals in Star Forming Galaxy

Spiral Galaxy NGC 253. Credit: ESO Astronomers found a rich molecular reservoir in the heart of an active star-forming galaxy with the Atacama Large Millimeter/submillimeter Array (ALMA). Among eight clouds identified at the center of the galaxy NGC 253, one exhibits very complex chemical composition, while in the other clouds many signals are missing. This chemical richness and diversity shed light on the nature of the baby boom galaxy. Ryo Ando, a graduate student of the University of Tokyo, and his colleagues observed the galaxy NGC 253 and for the first time, they resolved the locations of star formation in this galaxy down to the scale of a molecular cloud, which is a star formation site with a size of about 30 light-years. As a result, they identified eight massive, dusty clouds aligned along the center of the galaxy. “With its unprecedented resolution and sensitivity, ALMA showed us the detailed structure of the clouds,” said Ando, the lead author of the research paper...

Fermi Bubbles

Image: A giant gamma-ray structure was discovered in 2010 by processing Fermi all-sky data at energies from 1 to 10 billion electron volts, shown here. The dumbbell-shaped feature (center) emerges from the galactic center and extends 50 degrees north and south from the plane of the Milky Way, spanning the sky from the constellation Virgo to the constellation Grus. Credits: NASA/DOE/Fermi LAT/D. Finkbeiner et al. At a time when our earliest human ancestors mastered walking upright the heart of our Milky Way galaxy underwent a titanic eruption, driving gases and other material outward at 2 million miles per hour.

SpaceTime

Search This Blog