Aging star's weight loss secret revealed

November 25, 2015

VY Canis Majoris is a stellar goliath, a red hypergiant, one of the largest known stars in the Milky Way. It is 30-40 times the mass of the Sun and 300 000 times more luminous. In its current state, the star would encompass the orbit of Jupiter, having expanded tremendously as it enters the final stages of its life.

The new observations of the star used the SPHERE instrument on the VLT. The adaptive optics system of this instrument corrects images to a higher degree than earlier adaptive optics systems. This allows features very close to bright sources of light to be seen in great detail [1]. SPHERE clearly revealed how the brilliant light of VY Canis Majoris was lighting up clouds of material surrounding it.

And by using the ZIMPOL mode of SPHERE, the team could not only peer deeper into the heart of this cloud of gas and dust around the star, but they could also see how the starlight was scattered and polarised by the surrounding material. These measurements were key to discovering the elusive properties of the dust.

Careful analysis of the polarisation results revealed these grains of dust to be comparatively large particles, 0.5 micrometres across, which may seem small, but grains of this size are about 50 times larger than the dust normally found in interstellar space.

Throughout their expansion, massive stars shed large amounts of material -- every year, VY Canis Majoris sees 30 times the mass of the Earth expelled from its surface in the form of dust and gas. This cloud of material is pushed outwards before the star explodes, at which point some of the dust is destroyed, and the rest cast out into interstellar space. This material is then used, along with the heavier elements created during the supernova explosion, by the next generation of stars, which may make use of the material for planets.

Until now, it had remained mysterious how the material in these giant stars' upper atmospheres is pushed away into space before the host explodes. The most likely driver has always seemed to be radiation pressure, the force that starlight exerts. As this pressure is very weak, the process relies on large grains of dust, to ensure a broad enough surface area to have an appreciable effect [2].

"Massive stars live short lives," says lead author of the paper, Peter Scicluna, of the Academia Sinica Institute for Astronomy and Astrophysics, Taiwan. "When they near their final days, they lose alot of mass. In the past, we could only theorise about how this happened. But now, with the new SPHERE data, we have found large grains of dust around this hypergiant. These are big enough to be pushed away by the star's intense radiation pressure, which explains the star's rapid mass loss."

The large grains of dust observed so close to the star mean that the cloud can effectively scatter the star's visible light and be pushed by the radiation pressure from the star. The size of the dust grains also means much of it is likely to survive the radiation produced by VY Canis Majoris' inevitable dramatic demise as a supernova [3]. This dust then contributes to the surrounding interstellar medium, feeding future generations of stars and encouraging them to form planets.
-end-
Notes

[1] SPHERE/ZIMPOL uses extreme adaptive optics to create diffraction-limited images, which come a lot closer than previous adaptive optics instruments to achieving the theoretical limit of the telescope if there were no atmosphere. Extreme adaptive optics also allows much fainter objects to be seen very close to a bright star.

The images in the new study are also taken in visible light -- shorter wavelengths than the near-infrared regime, where most earlier adaptive optics imaging was performed. These two factors result in significantly sharper images than earlier VLT images. Even higher spatial resolution has been achieved with the VLTI, but the interferometer does not create images directly.

[2] The dust particles must be large enough to ensure the starlight can push it, but not so large that it simply sinks. Too small and the starlight would effectively pass through the dust; too large and the dust would be too heavy to push. The dust the team observed about VY Canis Majoris was precisely the right size to be most effectively propelled outwards by the starlight.

[3] The explosion will be soon by astronomical standards, but there is no cause for alarm, as this dramatic event is not likely for hundreds of thousands of years. It will be spectacular as seen from Earth -- perhaps as bright as the Moon -- but not a hazard to life here.

More information

This research was presented in a paper entitled "Large dust grains in the wind of VY Canis Majoris", by P. Scicluna et al., to appear in the journal Astronomy & Astrophysics.

The team is composed of P. Scicluna (Academia Sinica Institute for Astronomy and Astrophysics, Taiwan), R. Siebenmorgen (ESO, Garching, Germany), J. Blommaert (Vrije Universiteit, Brussels, Belgium), M. Kasper (ESO, Garching, Germany), N.V. Voshchinnikov (St. Petersburg University, St. Petersburg, Russia), R. Wesson (ESO, Santiago, Chile) and S. Wolf (Kiel University, Kiel, Germany).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world's most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world's most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world's largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become "the world's biggest eye on the sky".

Links

Research paper - http://www.eso.org/public/archives/releases/sciencepapers/eso1546/eso1546a.pdf

Link to ESOcast about polarimetry - http://www.eso.org/public/videos/esocast76a/

Photos of the VLT - http://www.eso.org/public/images/archive/category/paranal/

Contacts

Peter Scicluna
Academia Sinica Institute for Astronomy and AstrophysicsTaiwan
Tel: +886 (02) 2366 5420
Email: peterscicluna@asiaa.sinica.edu.tw

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org

ESO

Related Pressure Articles from Brightsurf:

A pressure sensor at your fingertips
Researchers have developed an ultrathin pressure sensor that can be attached directly to the skin.

High blood pressure treatment linked to less risk for drop in blood pressure upon standing
Treatment to lower blood pressure did not increase and may decrease the risk of extreme drops in blood pressure upon standing from a sitting position.

Changes in blood pressure control over 2 decades among US adults with high blood pressure
National survey data were used to examine how blood pressure control changed overall among U.S. adults with high blood pressure between 1999-2000 and 2017-2018 and by age, race, insurance type and access to health care.

Effect of reducing blood pressure medications on blood pressure control in older adults
Whether the amount of blood pressure medications taken by older adults could be reduced safely and without a significant change in short-term blood pressure control was the objective of this randomized clinical trial that included 534 adults 80 and older.

Brain pressure controls eye pressure, revealing new avenues for glaucoma treatment
Neuroscientists have discovered that eye and brain pressure are physiologically connected.

A question of pressure
The Physikalisch-Technische Bundesanstalt (PTB) has implemented a novel pressure measurement method, as a byproduct of the work on the 'new' kelvin.

Volcanoes under pressure
When will the next eruption take place? Examination of samples from Indonesia's Mount Merapi show that the explosivity of stratovolcanoes rises when mineral-rich gases seal the pores and microcracks in the uppermost layers of stone.

Here's something that will raise your blood pressure
The apelin receptor (APJ) has been presumed to play an important role in the contraction of blood vessels involved in blood pressure regulation.

Under time pressure, people tell us what we want to hear
When asked to answer questions quickly and impulsively, people tend to respond with a socially desirable answer rather than an honest one, a set of experiments shows.

Arm cuff blood pressure measurements may fall short for predicting heart disease risk in some people with resistant high blood pressure
A measurement of central blood pressure in people with difficult-to-treat high blood pressure could help reduce risk of heart disease better than traditional arm cuff readings for some patients, according to preliminary research presented at the American Heart Association's Hypertension 2019 Scientific Sessions.

Read More: Pressure News and Pressure Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.