A new NASA mission proposes to examine the nature of these neutron stars as well as how accurately we can use these beacons as celestial guiding points for deep space missions.
Pulsars spin at a dizzying rate of anywhere from seconds to milliseconds. As they whip around in their rotation, the hotspots flash periodically within sight of Earth. X-ray brightness from the pulsar increases when the hotspots comes within view, then dims as the hotspots turn away.
(There are a) millisecond class of pulsars that spin as rapidly as 700 times a second.These pulsars have such a consistent rotation rate that they are considered accurate celestial clocks. In space, they could be used in a similar way to global positioning satellites that provide navigation data to the military and civilians, particularly in vehicles.
Sen—Spinning in space are incredibly dense stars that shoot out X-rays at a predictable rate, like a lighthouse. A new NASA mission proposes to examine the nature of these neutron stars – also known as ‘pulsars’ – as well as how accurately we can use these beacons as celestial guiding points for deep space missions.Called NICER (Neutron Star Interior Composition Explorer) the mission will use X-rays to look at emissions from these strange stars. The instrument will launch in 2017. It will be mounted on the International Space Station for observations from low Earth orbit.Neutron stars are thought to form after the collapse of a massive star that is between 8 and 30 times the size of the sun, according to the University of Maryland’s Coleman Miller, an astronomy researcher. After the supernova blows off most of its mass, what is left behind is a small core about the size of New York City, at 20 kilometres (12 miles) across.In this small space, the protons and electrons that make up matter are “literally scrunched together”, stated NASA. One sugar-cube-sized bit of neutron star has a mass of a billion tons, the equivalent of Mount Everest’s weight, the agency added.Zaven Arzoumanian of NASA’s Goddard Space Flight Center, is deputy principal investigator for NICER. He told Sen: “Everything in our world is made of atoms consisting of protons and neutrons making up the nucleus plus electrons in orbit around it. But they are mainly empty space.”If you squeezed some gold, uranium or lead so hard that you eliminated all the empty space, you’d have something just like a neutron star. We want to understand how stuff behaves at such incredibly high densities.”
NICER is one of NASA’s astrophysics explorer-class missions that aim to examine the universe at low cost. This will cap NICER’s mission costs at just US$55 million (£39.2 million). Simulataneously with NICER’s announcement, the agency also said it will fund the Transiting Exoplanet Survey Satellite for US$200 million (£130.7 million).
The NICER instrument will include 56 small X-ray telescopes packed into a mini fridge-sized package. It will probably arrive at station in a Dragon cargo spacecraft manufactured and operated by SpaceX.
Once ready, the telescope array will examine X-rays that come from “hotspots” on the star’s surface, as well as its magnetic field, NASA stated. Pulsars spin at a dizzying rate of anywhere from seconds to milliseconds. As they whip around in their rotation, the hotspots flash periodically within sight of Earth. X-ray brightness from the pulsar increases whn the hotspots comes within view, then dims as the hotspots turn away.
NICER will focus on the millisecond class of pulsars that spin as rapidly as 700 times a second. These pulsars have such a consistent rotation rate that they are considered accurate celestial clocks. In space, they could be used in a similar way to global positioning satellites that provide navigation data to the military and civilians, particularly in vehicles.
“To demonstrate the navigation technology’s viability, the NICER … payload will use its telescopes to detect X-ray photons within these powerful beams of light to estimate the arrival times of their pulses,” NASA stated.
“With these measurements, the system will use specially developed algorithms to stitch together an on-board navigation solution.”
COSMIC LIGHTHOUSES WILL GUIDE SPACESHIPS THROUGH THE GALAXY
AMANDA DOYLE 02 APRIL 2012 00:00
Sen— Scientists have proposed using pulsars – ‘cosmic lighthouses’ – as a way of navigating future space missions.Space navigation currently relies on communications with Earth which can become problematic at large distances from the planet, but the proposed star navigation based on pulsar signals would make deep space exploration more feasible.Stars have always been important for navigation, and mariners have lobang been using the night sky to find their way. Many satellites and spacecraft also have star trackers which monitor the positions of the constellations so that they can automatically adjust their orientation. However, star trackers cannot achieve sufficient accuracy for deep space missions. In addition, the constellations will not retain their familiar patterns if one were to travel far beyond the Solar System.Currently spacecraft are tracked by radio telescopes on Earth, but this has major flaws. As light can only travel at a finite speed, it takes time to send a signal to Earth and back again to determine the spacecraft’s position. For example, a signal from NASA’s Voyager 1 would take around 30 hours to do a round trip.In addition, the further one travels from Earth, the larger the errors in the measured location will be. There will be an error of four kilometres for every Astronomical Unit travelled, where an Astronomical Unit is the distance between the Sun and the Earth (150 million kilometres). Thus for the likes of Voyager 1, which is at a distance of around 120 Astronomical Units from Earth, we can only pinpoint its location to within 480 kilometres.Neither of these facts are particularly comforting to any future deep space astronauts, so how can we can get around this problem? Professor Werner Becker from the Max-Planck-Institut für extraterrestrische Physik discussed a possible solution at the National Astronomy Meeting in Manchester, England, last week.Becker has suggested using cosmic lighthouses, known as pulsars, as navigational aids. A pulsar is a “dead” star which ended its adult life in a massive explosion known as a supernova. After many of the outer layers of the star get blown away, an extremely dense, compact core known as a neutron star is left behind. Neutron stars emit beams of radiation from their poles, and if one of these beams sweeps past Earth, akin to beams from a lighthouse, then the star is known as a pulsar.Pulsars have periodic signals, and will gradually spin down over time. However, Becker’s calculations take this reduction in rotation rate into account to produce accurate measurements. “The periods can be measured with accuracy which compares with atomic clocks, and this includes all the measurements of the spin down,” Becker told Sen. “Then you can predict the pulse arrival time over quite a long time.”
There are several different types of pulsars, but the ones best suited for the job are milli-second pulsars, which have extremely rapid rotation rates. “We concentrated on the milli-second pulsars for the purpose that they have the shortest periods which allows you to probe the distance with the highest accuracy,” explained Becker.
Knowing the exact time at which to expect a beam from a pulsar to arrive at Earth, and then comparing this to the time that the beam swept past a distant spacecraft, allows the location of the craft to be determined. Becker explained how the time difference in pulses can be extrapolated to find differences in distances.
“When we compare the pulse arrival time, we know where it should have been and where we measured it, and the difference in arrival time can be used (if multiplied by the velocity [of the spacecraft] and period of the pulsar) to compute the distance from the position you assumed you were during the measurement and where you were actually during the measurement. Then you correct your position according to your measurement and you do a new measurement. So it’s a kind of iterative process.”
The pulses as measured from Earth would also need to be corrected to the Solar System barycentre, i.e. the centre of mass of the Solar System, to take into account the different locations of radio telescopes.
As well as interstellar space, pulsar navigation could also be used for space exploration in the Solar System to provide back-up to Earth based systems. “The next step is going to Mars, and then you may ask the question do you really want to rely on being tracked only from Earth,” said Becker. If communications failed between Earth and a spacecraft en route to Mars, then the astronauts would be forced to navigate using the constellations. However, using this new system they would be able to navigate independent of radio communications with Earth.
Timing the signals from pulsars can also have applications much closer to home, as it can be used to assist current GPS satellites and the upcoming Galileo satellite navigation system, and Becker explained the advantages to this.
“These satellites are also controlled from Earth, and if you don’t control and correct the orbits of the GPS satellites for longer than 72 hours the signals get completely unreliable. It needs a control from the Earth, but if you have a satellite using this pulsar method and technology, you could use this to augment the GPS satellites or the Galileo satellites and they would refer to this external satellite doing the navigation. It would mean that you would not have any requirement to control the satellites any more from Earth; it would make it really autonomous.”
Astronomers have been collecting data on pulsars for decades, so some milli-second pulsars have already been timed to high precision. The next step for the pulsar navigation method is to design the technology that will allow it to be used aboard a spacecraft, and simulations are already being implemented to discover the best way to do this.
tem will use specially developed algorithms to stitch together an on-board navigation solution.”
photo credit: 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 / Swinburne Astronomy Productions/CAASTRO
An international team of astronomers has made a precise measurement of a distant, spinning star that’s about a million times more precise than the previous world’s best. That resolution is like being able to see DNA’s double helix structure from the moon.
“Compared to other objects in space, neutron stars are tiny,” Jean-Pierre Macquart from Curtin University explains in a news release. They’re about tens of kilometers in diameter. “So we need extremely high resolution to observe them and understand their physics.” Neutron stars are particularly interesting for astronomers because some of them (called pulsars) gave off pulsed radio waves whose beams regularly sweep across telescopes. Nearly five decades since pulsars were discovered, astronomers still don’t understand how they emit those pulses.
To get this highest resolution yet, Macquart, Ue-Li Pen of the Canadian Institute of Theoretical Astrophysics, and colleagues used the interstellar medium — the turbulent “empty” spaces in between, where charged particles float around — as a giant magnifying glass to look at the radio waves emitted by a small, spinning neutron star called PSR 0834+06.
These pulse signals become distorted as they pass through the interstellar medium. The team was able to use the distortions to reconstruct a close-up view of the pulsar from thousands of individual images of the scattering speckle pattern.
“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,” Macquart explains. By combining views from several telescopes, the previous record had a resolution of 50 microarcseconds.
The new record using this “interstellar lens,” the galaxy’s biggest telescope, is 50 picoarcseconds, or a million times more detail. And it resolves areas of less than 5 kilometers in the emission region. Because of that, the team found that the emission region of pulsar B0834+06 was much smaller than previously assumed and possibly much closer to the star’s surface — a critical piece of information for understanding the origin of the radio wave emission.
The work was published in Monthly Notices of the Royal Astronomical Society.