Formation of jets during the death of stars

Main Point:

Astronomers have found that only “strongly interacting” binary stars have the ability to end with powerful, bipolar jets of gas and dust.

Published in:

Monthly Notices of the Royal Astronomical Society

Study Further:

Nebula:

Nebula refers to a region or cloud of interstellar dust and gas appearing variously as a hazy bright or dark patch. It is also called as nebulosity.

Supernova:

Supernova refers to a catastrophic explosion of a large star in the latter stages of stellar evolution, with a resulting short-lived luminosity from 10 to 100 million times that of the Sun.

Usually, large stars come to an end with huge supernovae and smaller stars come to an end with planetary nebulae that were once thought to be spherical but now have also been found to end up with bipolar jets of gas and dust.

Binary Star:

It refers to a pair of stars that revolve around their common center of mass under mutual gravitational attraction.

Present Study:

In the present study, astronomers have found that only binary stars or a star with a massive planet have the ability to produce powerful jets of gas and dust at the time of their ending.

Usually, smaller stars begin to expand, when the hydrogen starts ending. Then they become Asymptotic Giant Branch (AGB) stars. They can stay in this phase for about 100,000 years. Some of these AGB stars become “pre-planetary” nebula, which are aspherical.

“What happens to change these spherical AGB stars into non-spherical nebulae, with two jets shooting out in opposite directions?” asked Eric Blackman, professor of physics and astronomy at Rochester. “We have been trying to come up with a better understanding of what happens at this stage.”

Astronomers think that AGB stars are not single stars but they are a part of binary system to form jets in the nebulae. Jets are probably produced as a result of the ejection of material first pulled from one object to the other and moved into a so-called accretion disk.

From University of Rochester,

Only two types of accretion models, both of which involve the most strongly interacting binaries, could create these jetted pre-planetary nebulae. In the first type of model, the “Roche lobe overflow,” the companions are so close that the AGB stellar envelope gets pulled into a disk around the companion. In the second type of models, or “common envelope” models, the companion is even closer and fully enters the envelope of the AGB star so that the two objects have a “common” envelope. From within the common envelope, very high accretion rate disks can either form around the companion from the AGB star material, or the companion can be shredded into a disk around the AGB star core. Both of these scenarios could provide enough energy and momentum to produce the jets that have been observed.

“Presently, jets in only a few per cent of known PPN have been studied and the overall fraction of PPN with jets, let alone the distribution of momenta among them, is not well constrained,” Astronomers wrote in the paper. “The potentially provocative utility of the present approach helps to motivate more PPN kinematic survey data, more binary searches and more theoretical/numerical simulation constraints on accretion rates.”

Sources:

How Stellar Death Can Lead To Twin Celestial Jets – University of Rochester (http://goo.gl/OTHVWD)

Eric G. Blackman, Scott Lucchini (2014). Using kinematic properties of pre-planetary nebulae to constrain engine paradigms Monthly Notices of the Royal Astronomical Society DOI: 10.1093/mnrasl/slu001