Skip to main content

NEW MACRONOVA'S MODEL


Image: The sequence illustrates the macronova model for the formation of a short-duration gamma-ray burst. 1. A pair of neutron stars in a binary system spiral together. 2. In the final milliseconds, as the two objects merge, they kick out highly radioactive material. This material heats up and expands, emitting a burst of light called a macronova. 3. The fading fireball blocks visible light but radiates in infrared light. 4. A remnant disk of debris surrounds the merged object, which may have collapsed to form a black hole Credit: NASA, ESA, and A. Feild (STScI)

A macronova (also called a 'kilonova' or an 'r-process supernova') occurs when two neutron stars or a neutron star and a black hole merge. It is a near-infrared/optical transient powered by the radioactive decay of heavy elements synthesized in the ejecta (~10-4-10-1 Msun with velocities ~ 0.1-0.3c) of a compact binary merger. Strong electromagnetic radiation is emitted due to the decay of heavy r-process ions that are produced and ejected fairly isotropically during the merger process-similar to a faint, short-lived supernova.


In the final milliseconds before the explosion, the two stars merge into a death spiral that kicks out highly radioactive material. This material heats up and expands, emitting a burst of light. The resulting "kilonova" is about 1,000 times brighter than a regular nova, which is caused by the eruption of a white dwarf.

The inspiral and merging of these compact objects are thought to be a strong source of gravitational waves (GWs). Macronova is also thought to be the progenitor of short gamma-ray bursts and the predominant source of stable r-process elements in the Universe.

These images taken by NASA's Hubble Space Telescope reveal a new type of stellar explosion produced from the merger of two compact objects. Hubble spotted the outburst while looking at the aftermath of a short-duration gamma-ray burst, a mysterious flash of intense high-energy radiation that appears from random directions in space. Short-duration blasts last at most a few seconds. They sometimes, however, produce faint afterglows in visible and near-infrared light that continue for several hours or days and help astronomers pinpoint the exact location of the burst.
In the image at left, the galaxy in the center produced the gamma-ray burst, designated GRB 130603B. The galaxy, cataloged as SDS J112848.22+170418.5, resides almost 4 billion light-years away. A probe of the galaxy with Hubble's Wide Field Camera 3 on June 13, 2013, revealed a glow in near-infrared light at the source of the gamma-ray burst, shown in the image at top, right. When Hubble observed the same location on July 3, the source had faded, shown in the image at below, right. The fading glow provided key evidence that it was the decaying fireball of a new type of stellar blast called a kilonova. Credit: NASA, ESA, N. Tanvir (University of Leicester), A. Fruchter (STScI), and A. Levan (University of Warwick)

The r-process is a nucleosynthesis process that occurs in supernovae and is responsible for the creation of approximately half of the neutron-rich atomic nuclei heavier than iron. The process entails a succession of rapid neutron captures (hence the name r-process) by heavy seed nuclei, typically 56Fe or other more neutron-rich heavy isotopes.

In a recent paper (Kisaka, Ioka & Nakar 2016, ApJ) the authors analyze the macronova observed as a infrared excess  several days after short gamma-ray burst GRB 130603B. They propose a new emission model in which the X-ray excess gives rise to the simultaneously observed infrared excess via thermal re-emission.

Schematic picture of the X-ray-powered model.


The X-ray-powered model explains the macronova with smaller ejecta mass. The new model is not based on the r-processes and can explain the X-ray and infrared excesses with a single energy source by the central engine like a black hole.


All posts here>> Home
 


Related posts 
Etichette:

Comments

Post a Comment

Popular posts from this blog

ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).
Post a Comment
Read more

ABOUT THE FORMATION OF THE COLD CLASSICAL KUIPER BELT

Image: The Kuiper Belt. Credit: NASA . The Kuiper belt is a circumstellar disc in the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun. It is similar to the asteroid belt (the circumstellar disc located roughly between the orbits of the planets Mars and Jupiter), but it is far larger-20 times as wide and 20 to 200 times as massive.
2 comments
Read more

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.
Post a Comment
Read more