Astronomers at NUI Galway’s Centre for Astronomy have made what is being viewed as an important breakthrough in the understanding of how pulsars (rapidly rotating neutron stars) work – a 40-year old problem that has mystified astronomers up to now.
The team, led by National University of Ireland, Galway’s Dr Andy Shearer, recently published its findings in the Monthly Notices of the Royal Astronomical Society. Speaking today, Shearer said the pulsars breakthough will be the foundation stone for future discoveries about stars and in the areas of fundamental science and astro physics.
"We are trying to do fundamental science, which, by its nature is very expensive. But if we can do this via numerical simulations and computations, it is a way in which Ireland can contribute to fundamental physics in a way we can afford."
Despite over 40 years of observation and theory, pulsars, which are highly magnetised rapidly rotating neutron stars, have defied an explanation of how they work, said the team.
Pulsars – which emit a beam of electromagnetic radiation that can only be observed when the emission beam points towards the Earth – are formed during a massive explosion at the end of a star’s life known as a Type II supernova.
"What happens is a star that is maybe 10 times the mass of the sun. When they reach the end of their life they tend to explode in an enormous explosion – probably the biggest explosion known. One star exploding will outshine its host galaxy, which may have a 100bn stars in it."
He said that massive explosion leaves behind a very dense star known as a neutron star.
"That’s one and a half times the mass of the sun, but it’s the size of Galway. It would fit into Galway Bay. It is very dense and represents the last state of normal matter. If it was any denser or smaller it would become a black hole, but it stays as a neutron star.
"We think that there are probably lots of neutron stars out there but because they are so small, they are difficult to see."
Shearer said astronomers want to understand, firstly, from the astro physics side, how many neutron stars are out there and eventually how do stars evolve.
"That will give us an understanding of how galaxies evolve. The other thing is we want to try understand how matter works at extremes. A neutron is one very big atom. The gravity is extremely strong so it gives us an understanding about the way in which general relativity works – basically extreme physics. In that way we can begin to understand a lot of the fundamental forces of nature."
Shearer said the pulsars discovery will help us understand the way in which plasmas – the full state of matter – work. "There’s a plasma around the earth, there’s a plasma around the sun. So if we can understand how plasmas work that might have implications in the future for many different areas, ranging from weather forecasting to energy generation, but it is a long way ahead."
This advancement at NUI Galway comes in the wake of last week’s news that astronomers at Swinburne University of Technology in Melbourne had discovered a new planet – "Planet Bling" – apparently composed entirely out of diamond and half as wide as Planet Jupiter.
Crab pulsar formed in 1054 and observed by Irish monks
But back to Galway, where the astronomers achieved their finding by comparing optical observations with a detailed model of the structure of the Crab pulsar, which was formed in April 1054 when it was observed as a daytime star.
Unusually, very few observations of this event come from Europe, although it was observed by Irish monks and recorded in the Irish Annals in the 11th century, explained Shearer.
From its observations, and using its inverse mapping or reverse engineering approach, Shearer said the team was able to establish for the first time that most of the light from the pulsar comes from close to the star’s surface.
This is contrary to most pulsar models and points to a new way of analysing observational data from pulsars, he explained.
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope opened a new era for pulsar astronomy, according to the NUI Galway astronomers.
“They represent extreme matter. They have a magnetic field, which can be greater than a million billion times stronger than the Earth’s magnetic field. Their density is also about a million, billion times greater than the density of the Earth."
Supercomputers fused with numerical models
Speaking today, Shearer explained how the findings have come after 10 years of enduring work at NUI Galway’s Centre for Astronomy: “Our success is based upon having some talented postgraduate students and postdoctoral researchers combined with looking at the problem in a different way. The result shows the importance of our approach of combining numerical models run on large supercomputers with detailed observations."
While he original computers were brought under the Cosmo Grid project, funded by the HEA , a project that ended in 2008, Shearer said that since then there’s been the E-Inis project.
"That has funded the supercomputers we are currently using, one of which is located at NUI Galway. Computationally they are big. We use the Irish Centre for High End Computing (ICHEC) – they manage the supercomputers. The other supercomputers are at UCD. The one in Galway is the back-up computer for weather forecasting."
He said that to follow these calculations the team will use the Science Foundation Ireland (SFI)-funded Galway Astronomical Stokes Polarimeter (GASP) to "finally establish the conditions around a pulsar and solve a 40-year old problem – how do pulsars work?"
Wide-angle view of 200-inch Hale Telescope in southern California. (Kardel). Image courtesy of www.astro.caltech.edu
GASP – heading to the Hale telescope in southern California
GASP is a camera that has been designed and built by astronomers at NUI Galway. Its design and construction was funded by two grants from SFI. GASP measures linear and circular polarisation from astronomical objects on very short timescales and Shearer said it is suited to be able to measure for the first time both the linear and circular polarisation from rapidly rotating pulsars.
In the future, after final telescope tests in Italy, GASP will be mounted on the 200-inch (five-metre) Hale telescope on Mount Palomar in southern California, where it will observe astronomical objects, including pulsars and other neutron stars. Hale was the world’s largest effective telescope for 45 years, between 1948 and 1993.
X-ray bright tail discovery with Italian, UK and US astronomers
In another development, NUI Galway astronomers, working with colleagues in Italy, the UK and US, have discovered an X-ray bright tail coming from a pulsar.
The tail was discovered by combining optical observations taken with the European Southern Observatory’s Very Large Telescope and NASA’s Chandra X-Ray observatory.
Shearer said the pulsar, known as PSR J0357, is about half a million years old and is located 1,600 light years from Earth with a tail of over four light years across.
These findings have been recently published in The Astrophysical Journal.