Mark Thompson, Author at Universe Today

November 19, 2010December 24, 2015 by Mark Thompson

Twinkle Twinkle Little Missing Stars, How I Wonder Where you are?

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‘Twinkle twinkle little star, how I wonder what you are?’ This nursery rhyme is one of the best loved around the World. For astronomers though, stars can be a bit more of a nightmare, not only in understanding their complex evolutionary processes but also and perhaps more simply, figuring out how many there are. Until now there has been a gross mismatch between the number of stars that are found within our galaxy, the Milky Way and the amount that astronomer think should be there. In short, where are the missing stars?

The Milky Way is joined by about 30 other galaxies that make up our local group of galaxies, including the Andromeda Galaxy and according to current theories there should be about 100 billion stars in each. The calculations are based on the rate of star birth in the Milky Way, about 10 new stars per year. But according to Dr Jan Pflamm-Altenburg of the Argelander Institute for Astronomy at the University of Bonn “Actually, it would give many more stars than we actually see” and therein lies the problem.

The recent study by Dr Pflamm-Altenburg and Dr. Carsten Weidner of the Scottish St. Andrews University suggests that perhaps the estimated rate of star birth being used to calculate the number of stars could simply be too high. With galaxies in our Local Group its relatively easy to just count the number of new stars that can be seen but for more distant galaxies, they are too far away for individual stars to be seen.

By studying the nearby galaxies, Pflamm-Altenburg and Weidner discovered that for every 300 young small stars, there seems to be one large massive new star and fortunately this seems to be universal. Due to the unique nature of the massive young stars, they leave a tell tail sign in the light of distant galaxies so even though they cannot be individually identified they can still be detected and the strength of the signal determines the number of massive stars. Multiply by the number of massive stars by this ratio of 300 and the actual rate of stellar birth can be calculated.

It seems though that this rate has varied over the history of the Universe and dependent on the amount of ‘space’ available in the vicinity of the star formation. If there is a baby boom in star formation then a higher number of heavies seem to form in a theory called ‘stellar crowding’. When stars form, they form as clusters rather than individual stars but it seems that the overall mass of the group is the same, regardless of how many star embryo’s there really are. When star birth is at a high rate, space can be limited so larger more massive stars tend to form compared to smaller stars.

Massive galaxies like this where star birth is booming are called “ultra-compact dwarf galaxies” (UCDs). Sometimes its possible in these galaxies that young stars can even fuse together to form larger stars so the large to small ratio can be around 1:50 instead of 1:300. This means we have been using the wrong figure and estimating far too high.

Using this new found figure, Pflamm-Altenburg and Weidner have recalculated the number of stars that ‘should’ be in a galaxy and compared to those that we can see and rather pleasantly, the numbers match! It seems that the conundrum of the missing stars that has been perplexing astronomers for decades has finally been resolved.

Source: University of Bonn

November 8, 2010December 24, 2015 by Mark Thompson

Solar Explosions Spark Controversy

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Nowhere in the Solar System are conditions more extreme than the Sun. Every second it converts millions of tons of matter into energy to create the intense levels of heat and light we expect of our local star. Study the Sun in different wavelengths and its violent nature can really become apparent. The STEREO satellite has been studying the Sun at a wavelength of 304Å and the results support a controversial solar theory.

Coronal Mass Ejections (or CMEs) are common on the Sun and they have a very real impact to us here on Earth. The solar explosions expel trillions of trillions of tons of super hot hydrogen gas into space, sometimes in the direction of the Earth. Traveling at speeds up to 2,000 kilometers per second it takes just a day for the magnetized gas to reach us and on arrival it can induce strong electric currents in the Earth’s atmosphere leading not only to the beautiful auroral displays but also to telecommunication outages, GPS system failures and even disturbances to power grids.

Solar flares, to use their other name, were first observed back in 1859 and since then, scientists have been studying them to try to understand the mechanism that causes the eruption. It has been known for some time that the magnetically charged gas or plasma is interacting with the magnetic field of the Sun but the detail has been at best, elusive.

In 2006, the international satellite STEREO was launched with the objective of continuously monitoring and studying the CMEs as they head toward the Earth and its data has helped scientists at the Naval Research Laboratory (NRL) in Washington, D.C., start to understand the phenomenon.

Using this new data, scientists at the NRL compared the observed activity with a controversial theory that was first proposed by Dr James Chen (also from the NRL) in 1989. His theory suggested that the erupting clouds of plasma are giant ‘magnetic flux ropes’, effectively a twisted up magnetic field line shaped like a donut. The Sun being a vast sphere of gas suffers from differential rotation where the polar regions of the Sun and the equatorial regions all rotate at different speeds. As a direct result of this, the plasma ‘drags’ the magnetic field lines around and the Sun and it gets more and more twisted up . Eventually, it bursts through the surface, taking some plasma with it giving us one of the most dramatic yet potentially destructive events in the Universe.

Dr Chen and a Valbona Kunkel, a doctorate student at George Mason University, applied Dr. Chen’s model to the new data from STEREO and found that the theory agrees with the measured trajectories of the ejected material. It therefore looks like his theory, whilst controversial may have been right all along.

Its strange to think that our nearest star, the Sun, still has secrets. Yet thanks to the work of Dr. Chen and his team, this one seems to have been unraveled and understanding the strange solar explosions will perhaps help us to minimise impact to Earth based technologies in years to come.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

October 27, 2010December 24, 2015 by Mark Thompson

Super Star Smashes into the Record Books.

Pulses from neutron star (rear) are slowed as they pass near foreground white dwarf. This effect allowed astronomers to measure masses of the system. CREDIT: Bill Saxton, NRAO/AUI/NSF

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The discovery of a super massive neutron star has thrown our understanding of stellar evolution into turmoil. The new star, called PSR J1614-2230 contains twice the mass of the Sun but compressed down into a star that is smaller than the Earth (you could fit over a million Earth’s inside the Sun by comparison). It is estimated a thimbleful of material from the star could weigh more than 500 million tons — that equates to about a million airliners. The study has cast serious doubt over how matter reacts under extreme densities.

The study by a team of astronomers using the National Radio Astronomy Observatory in New Mexico focussed its attention on the star which is about 3,000 light years away (the distance light can travel in 3,000 years at a speed of 300,000 km per second). The stellar corpse whose life ended long ago is now rotating at an incredible speed, completing 317 rotations every second. Its emitting an intense beam of energy from its polar regions which just happens to point in the direction of us here on Earth. We can detect this radiation beam as it flashes on and off like a celestial lighthouse. This type of neutron star is classed a pulsar.

Rather fortuitously, the star is part of a binary star system and is orbited by a white dwarf star which completes one orbit in just nine days. Its through the measurements of the interaction of the two which gave astronomers the clue as to the pulsar’s mass. The orbit of the white dwarf takes it between the beam of radiation and us here on Earth so that the energy from the beam has to pass close by the companion star. By measuring the delay in the beam’s arrival caused by distortion of space-time in the proximity of the white dwarf, scientists can determine the mass of both objects. Its an effect called the Shapiro Delay and its simply luck that the orientation of the stars to the Earth allows the effect to be measured.

Dave Finley, Public Information Officer from NRAO told Universe Today ‘Pulsars are neutron stars, whose radiation beams emerge from the poles and sweep across the Earth. The orientation of the poles (and thus of the beams) is a matter of chance. We just got very lucky with this system.’

The discovery which was made possible by the new ‘Green Bank Ultimate Pulsar Processing Instrument (GUPPI) was able to measure the pulses from the pulsar with incredible accuracy and thus come to the conclusion that the star weighed in at a hefty two times the mass of the Sun. Current theories suggested a mass of around one and a half solar masses were possible but this new discovery changes the understanding of the composition of such stars, even to the subatomic level.

Neutron stars or pulsars are extreme objects at the very edges of the conditions that matter can exist. They really test our knowledge of the physical Universe and slowly but surely, through dedicated work of teams of astronomers, we are not only learning more about the stars above our heads but more and more about matter in the Universe in which we live.

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro

Source: NRAO

October 13, 2010December 24, 2015 by Mark Thompson

Galaxy Growth Not Always Result of Violent Collisions

Artist’s impression of a young galaxy accreting material. Credit: ESO/L. Calçada

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Until recently, it was thought the galactic equivalent of a motorway pile-up was the only way galaxies got bigger. But startling new evidence from a European team of astronomers suggests that violent galactic collisions are not the only way that galaxies evolve and grow, and instead there seems to be something else happening that has affected the majority of galaxies — a kinder, gentler action which is not quite so disruptive.

For some years, astronomers have struggled to understand why the mass of galaxies seems to have increased dramatically just a few billion years after the Big Bang. We know from observation that galaxies collide but this is an incredibly violent activity and one that is not particularly common.

A new study using the Very Large Telescope (VLT) at the European Southern Observatory (ESO), by a team led by Giovanni Cresci, looked for evidence that galaxies might be accreting material from the hydrogen and helium gas that filled the early Universe and permeates the space between the galaxies. We know that they are surrounded by halos of unseen material but Cresci’s team wanted to see if there was any evidence of material being sucked into the galaxy from the surrounding environment.

Their study focused on a group of distant galaxies which would represent those in the early Universe, about 2 billion years after the big bang, to see if they could detect any evidence of this gas accretion.

Using the SINFONI (Spectrograph for Integral Field Observation in the Near Infrared) attached to the VLT, Cresci and his team mapped the distribution of elements within the target galaxies. Their findings showed that instead of heavier elements being concentrated around the core as we find in today’s galaxies, the core was surprisingly abundant of the lighter elements hydrogen and helium. This can only be as a result of accretion of lighter elements from the surrounding area boosting the rate of star formation in the core. The accretion process itself relies on cool gas being transferred directly into the core of the galaxy.

“The primordial gas in the halo of galaxies, especially at great distances, is mostly shock heated and therefore very hot,” Cresci told Universe Today. “To be accreted it has to be cooled and this is not an efficient process. Recent theoretical models have shown that narrow streams of cold gas can form, and that they are able to penetrate the hot gas and to provide fresh gas to the centre of the galaxy. Unlike more destructive and violent mergers between galaxies, the streams are likely to keep the rotating disk configuration intact, although turbulent.”

This new discovery means astronomers have perhaps found an answer to a long standing question but with the major consequence of needing to rewrite our current theories of the evolution of the Universe.

Source: ESO, email exchange with Cresci

Mark Thompson is a writer and the astronomy presenter on the BBC One Show. See his website, The People’s Astronomer, and you can follow him on Twitter, @PeoplesAstro