CAASTRO Astronomers Make precise measurement of neutron star

The densely packed matter of a pulsar spins at incredible speeds, and emits radio waves that can be observed from Earth, but how neutron stars emit these waves is still a mystery. 

Credit: Swinburne Astronomy Productions /CAASTRO.

An international team of astronomers has made a measurement of a distant neutron star that is one million times more precise than the previous world's best.

The researchers were able to use the interstellar medium (ISM), the 'empty' space between stars and galaxies that is made up of sparsely spread charged particles, as a giant lens to magnify and look closely at the radio wave emission from a small rotating neutron star.

This technique yielded the highest resolution measurement ever achieved, equivalent to being able to see the double-helix structure of our genes from the Moon!

"Compared to other objects in space, neutron stars are tiny – only tens of kilometres in diameter – so we need extremely high resolution to observe them and understand their physics," Dr Jean-Pierre Macquart from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) in Perth, Australia, said.

Dr Macquart, a member of the ARC Centre of Excellence for All-sky Astrophysics (CAASTRO), said neutron stars were particularly interesting objects to study, as some of them – called pulsars – gave off pulsed radio waves whose beams swept across telescopes at regular intervals.

"More than 45 years since astronomers discovered pulsars, we still don't understand the mechanism by which they emit radio wave pulses," he said.



A spinning neutron star emitting a stream of radio waves that appear as regular pulses when observed from Earth. Simulation credit to Swinburne Astronomy Productions /CAASTRO.

The researchers found they could use the distortions of these pulse signals as they passed through the turbulent interstellar medium (ISM) to reconstruct a close in view of the pulsar from thousands of individual sub-images of the pulsar.

"The best we could previously do was pointing a large number of radio telescopes across the world at the same pulsar, using the distance between the telescopes on Earth to get good resolution," Dr Macquart said.

The previous record using combined views from many telescopes was an angular resolution of 50 microarcseconds, but the team - led by Professor Ue-Li Pen of the Canadian Institute of Theoretical Astrophysics and a CAASTRO Partner Investigator, has now proven their 'interstellar lens' can get down to 50 picoarcseconds, or a million times more detail, resolving areas of less than 5km in the emission region.

"Our new method can take this technology to the next level and finally get to the bottom of some hotly debated theories about pulsar emission," Professor Pen said.

This new technique also opens up the possibilities for precise distance measurements to pulsars that orbit a companion star and 'image' their extremely small orbits, which is ultimately a new and highly sensitive test of Einstein's theory of General Relativity," Professor Pen said.

More information: Ue-Li Pen, Jean-Pierre Macquart, Adam T. Deller, and Walter Brisken. "50 picoarcsec astrometry of pulsar emission." MNRAS (May 01, 2014) Vol. 440 L36-L40 first published online February 14, 2014. DOI: 10.1093/mnrasl/slu010 . 

Also available on arXiv: http://adsabs.harvard.edu/abs/2014MNRAS.440L..36P

How would Earth communicate with a starship or a distant civilization?

USS Enterprise NCC-1701-D, a starship of the Star Trek: The Next Generation era. 

Credit: Memory-Alpha.Org /Paramount Pictures /CBS Studios

Its not a new question but its still a puzzle; How would humans communicate with extraterrestrials.

It may not be as easy as the science fiction writers and film makers would have us believe.

David Messerschmitt

David Messerschmitt, of the University of California at Berkeley, is addressing this potential problem. A new paper by him on Arxiv examines the issue and it provides an intriguing insight into how to communicate outside of our Earth.

Messerschmitt explains that humans already communicate with probes that are astronomical distances from Earth (Voyager 1, now in interstellar space) at radio frequencies, and there is some usage now of laser/optical communications (namely between the Earth and the moon).

Across greater distances, however, you lose information, the interstellar medium (ISM) gets in the way, and stars shift due to relative motion.

We are adept at communicating with our own satellites and probes but don't know how other civilizations communicate and how they design their systems. So, how could you send a message that would definitely be picked up and understood?

This sequence of images, showing a region where fewer stars are forming near the constellation of Perseus, illustrates how the structure and distribution of the interstellar medium can be distilled from the images obtained with Planck. 

Credit: ESA / HFI and LFI Consortia

Messerschmitt further explains that starships and civilizations would, almost certainly, have different communications protocols and therefore, requirements.

Starship communication would be two-way and based on a similar design, so success comes by having high "uplink and downlink transmit times".

The more information, the better it would be for scientific observations and keeping down errors.

Civilization-to-civilization chats, however, would present headaches. As with all diplomatic negotiations, crafting suitable messages would take time.

Then we'd have to send the message out repeatedly to make sure it is heard (which actually means that reliability is not as big of a problem.)

Then the interstellar medium  (ISM) would have to be contended with (something that pulsar astronomers and astrophysicists are already working on, he said).

In either case, when talking to starships or other civilizations, one can assume there'd be a lot of energy involved, he added.

"Starships are likely to be much closer than the nearest civilizations, but the cost of either a large transmit antenna or transmit energy is likely to be considerably greater for the starship than for a terrestrial-based transmitter," he said, suggesting that a solution would be to minimize the energy delivered to the receiver.

Other civilizations may have found more efficient ways to overcome this problem, he added.

You can read more details of the research on Arxiv, where Messerschmitt talks about Gaussian noise, channel coding and other parameters to keep in mind during communication.

More information: "Design for minimum energy in starship and interstellar communication." David G. Messerschmitt. arXiv:1402.1215 [astro-ph.IM] arxiv.org/abs/1402.1215