Students Discover Millisecond Pulsar, Help in the Search for Gravitational Waves

Using an array of millisecond pulsars, astronomers can detect tiny changes in the pulse arrival times in order to detect the influence of gravitational waves. Credit: NRAO

A special project to search for pulsars has bagged the first student discovery of a millisecond pulsar – a super-fast spinning star, and this one rotates about 324 times per second. The Pulsar Search Collaboratory (PSC) has students analyzing real data from the National Radio Astronomy Observatory’s (NRAO) Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. Astronomers involved with the project said the discovery could help detect elusive ripples in spacetime known as gravitational waves.

“Gravitational waves are ripples in the fabric of spacetime predicted by Einstein’s theory of General Relativity,” said Dr. Maura McLaughlin, from West Virginia University. “We have very good proof for their existence but, despite Einstein’s prediction back in the early 1900s, they have never been detected.”

Four other pulsars have been discovered by high school students participating in this project.

Pulsar hunters Sydney Dydiw of Trinity High School, Emily Phan of George C. Marshall High School, Anne Agee of Roanoke Valley Governor's School, and Jessica Pal of Rowan County High School. Not pictured: Max Sterling of Langley High School. Credit: NRAO

“When you discover a pulsar, you feel like you’re walking on air! It is the best experience you can ever have,” said student co-discoverer Jessica Pal of Rowan County High School in Kentucky. “You get to meet astronomers and talk to them about your experience. I still can’t believe I found a pulsar. It is wonderful to know that there is something out there in space that you discovered.”

The other student involved in the discovery was Emily Phan of George C. Marshall High School in Virginia, who along with Pal found the millisecond pulsar on January 17, 2012. It was later confirmed by Max Sterling of Langley High School, Sydney Dydiw of Trinity High School, and Anne Agee of Roanoke Valley Governor’s School, all in Virginia.

“I am considering pursuing astronomy as a career choice,” said Agee. “The Pulsar Search Collaboratory has opened my eyes to how fun astronomy can be!”

Once the pulsar candidate was reported to NRAO, a followup observing session was scheduled on the giant, 17-million-pound telescope. On January 24, 2012, observations confirmed that the pulsar was real.

Pulsars are spinning neutron stars that sling “lighthouse beams” of radio waves around as they rotate. A neutron star is what is left after a massive star explodes at the end of its “normal” life. With no nuclear fuel left to produce energy to offset the stellar remnant’s weight, its material is compressed to extreme densities. The pressure squeezes together most of its protons and electrons to form neutrons; hence, the name “neutron star.” One tablespoon of material from a pulsar would weigh 10 million tons.

On January 24, 2012, observations with the Green Bank Telescope at 800 MHz confirmed that the signal was astronomical and zeroed in on its position. Pulsars are brighter at lower frequencies (like 350 MHz, above) than at higher frequencies, and so the confirmation plot is noisier than the original data. Since this pulsar spins so fast, it may be used as part of the pulsar timing array used to detect gravitational waves. Courtesy NRAO.

The object that the students discovered is a special class of pulsars called millisecond pulsars, which are the fastest-spinning neutron stars. They are highly stable and keep time more accurately than atomic clocks.

Astronomers don’t know much about them, however. But because of their stability, these pulsars may someday allow astronomers to detect gravitational waves.

Millisecond pulsars, however, could hold the key to that discovery. Like buoys bobbing on the ocean, pulsars can be perturbed by gravitational waves.

“Gravitational waves are invisible,” said McLaughlin. “But by timing pulsars distributed across the sky, we may be able to detect very small changes in pulse arrival times due to the influence of these waves.”

Millisecond pulsars are generally older pulsars that have been “spun up” by stealing mass from companion stars, but much is left to discover about their formation.

“This latest discovery will help us understand the genesis of millisecond pulsars,” said Dr. Duncan Lorimer, who is also part of the project. “It’s a very exciting time to be finding pulsars!”

Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF

The PSC is a joint project of the National Radio Astronomy Observatory and West Virginia University, funded by a grant from the National Science Foundation. The PSC includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from the GBT.

Approximately 300 hours of the observing data were reserved for analysis by student teams. These students have been working with about 500 other students across the country. The responsibility for the work, and for the discoveries, is theirs. They are trained by astronomers and by their teachers to distinguish between pulsars and noise.

The PSC will continue through the 2012-2013 school year. Teachers interested in participating in the program can learn more at this link. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

How Well Can Astronomers Study Exoplanet Atmospheres?

Artist's impression of exoplanets around other stars. Credits: ESA/AOES Medialab

Exoplanet discoveries are happening at a frenetic pace, and some of the latest newly discovered worlds are sometimes described as “Earth-Like” and “potentially habitable.”

The basis of this comparison is, in many cases, based on the distance between the exoplanet and its host star. Unfortunately the distance between a planet and its host star is only half the picture. The other half is determining if an exoplanet has an atmosphere, and what the contents of said atmosphere may be.

Basically, just because an exoplanet is in the “habitable zone” around its host star, it may not necessarily be habitable. If an exoplanet has a thick, crushing, Venus-Like atmosphere, it would most likely be too hot for surface water. The opposite holds true as well, as it could be entirely possible for an exoplanet to have a thin, wispy Mars-like atmosphere where any water would be locked up as ice.

At this point, how well can astronomers study the atmosphere around an exoplanet?

The spectrum from a giant exoplanet, orbiting around the bright, young, star HR 8799. Image Credit: ESO/M. Janson

Currently, there are only a handful of methods researchers can use to make estimates of exoplanet atmospheres. Interestingly enough, one method makes use of the light coming from the host star. The basic principle is that the light from a star can be analyzed both before and after an exoplanet crosses in front of the star. By comparing the spectrum from the host star, and the spectrum of an exoplanet, the tell-tale signs of atmospheric contents can be detected.

Methods to detect the atmospheric composition of such distant worlds are fairly new, as shown by work done with the Spitzer Space Telescope and ESO’s Very Large Telescope

Recently, astronomers from The Sternberg Astronomical Institute at Moscow State University used data from the Hubble Space Telescope in an attempt to better detect atmospheres around exoplanets. Abubekerov and team created mathematical models to analyze light curves from distant stars. In the case of Abubekerov’s research, the selected star was HD 189733 – a K-class star a bit cooler and smaller than our Sun.

About 60 light-years from Earth, HD 189733 also happens to have a binary companion orbiting it at a radius of about 200 A.U. So far, one exoplanet is known to orbit HD 189733. Discovered in 2005, HD 189733 b is a roughly Jupiter-size exoplanet which orbits its host star in just over two days. While not mentioned directly in Abubekerov’s paper, other studies have detected methane, carbon monoxide, water vapor and sodium in HD 189733 b’s atmosphere.

Light curve from HD 189733 in 5500 - 6000 angstrom range.

By applying their models to the light curves from HD 189733, Abubekerov’s team was able to better understand how light at different wavelengths behaves when an exoplanet crosses in front of its host star.

According to Abubekerov and team, the end result of their research was unsuccessful. The team suspects dark spot activity on HD 189733 was a contributing factor to their models not agreeing with actual observations.

The team stressed that additional observational data from HD 189733 when spot activity is negligible would be required to further refine their work. Despite their models not being successful, the team is confident that exoplanet radius increases with decreasing wavelength, which may imply the presence of an atmosphere.

Research such as Abubekerov’s will help astronomers build better models and pave the way for “sniffing” exoplanet atmospheres. Newer technology such as the James Webb Space Telescope and the European Extremely Large Telescope will also provide better data. In the not-too-distant future, astronomers and astrobiologists should be able to examine the atmospheres of exoplanets in the habitable zone.

If you’d like to read the full research paper, you can access a pre-print version at:http://arxiv.org/pdf/1201.4043v1.pdf

New Insights into the Moon’s Mysterious Magnetic Field

Ever since the Apollo era, scientist have known that the Moon had some kind of magnetic field in the past, but doesn’t have one now. Understanding why is important, because it can tell us how magnetic fields are generated, how long they last, and how they shut down. New studies of Apollo lunar samples answer some of these questions, but they also create many more questions to be answered.

The lunar samples returned by the Apollo missions show evidence of magnetization. Rocks are magnetized when they are heated and then cooled in a magnetic field. As they cool below the Curie temperature (about 800 degrees C, depending on the material), the metallic particles in the rock line up along ambient magnetic fields and freeze in that position, producing a remnant magnetization.

This magnetization can also be measured from space. Studies from orbiting satellites show that the Moon’s magnetization extends well beyond the regions sampled by Apollo astronauts. All this magnetization means that the Moon must have had a magnetic field at some point in its early history.

Most of the magnetic fields we know of in the Solar System are generated by a dynamo. Basically, this involves convection in a metallic liquid core, which effectively moves the metal atoms’ electrons, creating an electric current. This current then induces a magnetic field. The convection itself is thought to be driven by cooling. As the outer core cools, the colder portions sink to the interior and let the warmer interior sections move outwards towards the exterior.

Because the Moon is so small, a magnetic dynamo that is driven by convective cooling is expected to have shut down some time around 4.2 billion years ago. So, evidence of magnetization after this time would need either 1) an energy source other than cooling to drive the motion of a liquid core, or 2) a completely different mechanism for creating magnetic fields.

Laboratory experiments have suggested one such alternate method. Large basin-forming impacts could produce short-lived magnetic fields on the Moon, which would be recorded in the hot materials ejected during the impact event. In fact, some observations of magnetization are located at the opposite side of the Moon (the antipode) from large basins.

So, how can you tell if magnetization in a rock was formed by a core dynamo or an impact event? Well, impact-induced magnetic fields last only about 1 day. If a rock cooled very slowly, it would not record such a short-lived magnetic field, so any magnetism it retains must have been produced by a dynamo. Also, rocks that have been involved in impacts show evidence of shock in their minerals.

One lunar sample, number 76535, which shows evidence of slow cooling and no shock effects, has a distinct remnant magnetization. This, along with the age of the sample, suggests that the Moon had a liquid core and a dynamo-generated magnetic field 4.2 billion years ago. Such a core dynamo is consistent with convective cooling. But, what if there are younger samples?

New studies recently published in Science by Erin Shea and her colleagues suggest this may be the case. Ms Shea, a graduate student at MIT, and her team studied sample 10020, a 3.7 billion year old mare basalt brought back by the Apollo 11 astronauts. They demonstrated that sample 10020 shows no evidence of shock in its minerals. They estimated that the sample took more than 12 days to cool, which is much slower than the lifetime of an impact-induced magnetic field. And they found that the sample is very strongly magnetized.

From their studies, Ms Shea and her colleagues conclude that the Moon had a strong magnetic dynamo, and therefore a moving metallic core, around 3.7 billion years ago. This is well after the time a convective cooling dynamo would have shut down. It is not clear, however, if the dynamo was continually active since 4.2 billion years ago, or if the mechanism that moved the liquid core was the same at 4.2 and 3.8 billion years. So, what other ways are there to keep a liquid core moving?

Recent studies by a team of French and Belgian scientists, led by Dr. Le Bars, suggest that large impacts can unlock the Moon from its synchronous rotation with the Earth. This would create tides in the liquid core, much like the Earth’s oceans. These core tides would cause significant distortions at the core-mantle boundary, which could drive large-scale flows in the core, creating a dynamo.

In another recent study, Dr. Dwyer and colleagues suggested that precession of the lunar spin axis could stir the liquid core. The early Moon’s proximity to the Earth would have made the Moon’s spin axis wobble. This precession would cause different motions in the liquid core and overlying solid mantle, producing a long-lasting (longer than 1 billion years) mechanical stirring of the core. Dr. Dwyer and his team estimate that such a dynamo would naturally shut down about 2.7 billion years ago as the Moon moved away from the Earth over time, diminishing its gravitational influence.

Unfortunately, the magnetic field suggested by the study of sample 10020 doesn’t fit either of these possibilities. Both these models would provide magnetic fields that are too weak to have produced the strong magnetization observed in sample 10020. Another method for mobilizing the liquid core of the Moon will need to be found in order to explain these new findings.

Sources:
A Long-Lived Lunar Core Dynamo. Shea, et al. Science 27, January 2012, 453-456.doi:10.1126/science.1215359.

A long-lived lunar dynamo driven by continuous mechanical stirring. Le Bars et al. Nature 479, November 2011, 212-214. doi:10.1038/nature10564.

An impact-driven dynamo for the early Moon. Dwyer et al. Nature 479, November 2011, 215-218. doi:10.1038/nature10565.

Help Astronomers Measure the Solar System!

The orbit of asteroid 433 Eros brings it close to Earth on Jan. 31. (www.astronomerswithoutborders.org)

As the bright Mars-crossing asteroid 433 Eros makes its closest approach to Earth since 1975, astronomers around the globe are taking the opportunity to measure its position in the sky, thereby fine-tuning our working knowledge of distances in the solar system. Using the optical principle of parallax, whereby different viewpoints of the same object show slightly shifted positions relative to background objects, skywatchers in different parts of the world can observe Eros over the next few nights and share their images online.

The endeavor is called the Eros Parallax Project, and you can participate too!

433 Eros' path from jan. 30 - Feb. 1, 2012. (transitofvenus.nl)

Discovered in 1898, Eros was the largest near-Earth asteroid yet identified. Its close and relatively bright oppositions were calculated by astronomers of the day and used, along with solar transits by Venus (one of which, if you haven’t heard, will also occur this year on June 5!) to calculate distances in the inner solar system.

Having both events take place within the same year offers today’s astronomers an unparalleled opportunity to obtain observational measurements.

Through the efforts of the Astronomers Without Borders organization, along with Steven van Roode and Michael Richmond from the Transit of Venus project, anyone with moderate astrophotography experience can participate in the observation of Eros and share their photos via free online software.

Using the data gathered by individual participants positioned around the world, each with their own specific viewpoints, astronomers will be able to precisely measure the distance to Eros.

The more accurately that distance is known, the more accurately the distance from Earth to the Sun can be calculated – via the orbital mechanics of Kepler’s third law.

The tumbling motion of elongated 33-km-long Eros creates a changing brightness. (via transitofvenus.nl)

The last time such a bright pass of Eros occurred was in January of 1931. Observations of the asteroid made at that time allowed astronomers to calculate a solar parallax of 8″ .790, the most accurate up to that time and the most accurate until 1968, when data acquired by radar measurements gave more detailed measurements.

In many ways the 2012 close approach by Eros – astronomically close, but still a very safe 16.6 million miles (26.7 million km) away – will allow for a re-eneactment of the 1931 event… with the exception that this time amateur skywatchers will also contribute data, instantly, from all over the world!

One has to wonder…when Eros comes this close again in 2056, what sort of technology will we use to watch it then…

Find out more about the Eros Parallax Project and how to participate here.

And be sure to check out the article about the project on Astronomers Without Borders as well.

Earth’s “Missing Energy”

Clouds play a vital role in Earth's energy balance, cooling or warming Earth's surface depending on their type. This painting, "Cumulus Congestus," by JPL's Graeme Stephens, principal investigator of NASA's CloudSat mission, depicts cumulus clouds, which transport energy away from Earth's surface. Image credit: Graeme Stephens

Like many of us, Earth works on a budget – an energy budget. However, this energy isn’t the type that powers our automobiles or electric lights. It’s the energy that empowers our living planet. When it comes to input and output, the Earth is a huge throughput system. The most massive source of incoming energy is solar radiation, with geothermal and tidal energy completing the circle. All of these forms of energy are converted to heat and re-radiated into space. In 2010, scientists at the National Center for Atmospheric Research in Boulder, Colorado publicized a study taken from satellite observations which stated there were certain variances between Earth’s heat and ocean heating. What they found was “missing energy” in our planet’s system. Why did this energy seem to be disappearing? The research group began wondering if perhaps there was a problem with the method of recording energy as absorbed from the Sun and its emission back to space.

This was a question that needed an answer. Enter an international team of atmospheric scientists and oceanographers, led by Norman Loeb of NASA’s Langley Research Center in Hampton, Virginia, and including Graeme Stephens of NASA’s Jet Propulsion Laboratory in Pasadena, California. It was their mission to account for the missing energy. Armed with 10 years of data from NASA Langley’s orbiting Clouds and the Earth’s Radiant Energy System Experiment (CERES) instruments, the team set out to record the radiation balance located at the apex of Earth’s atmosphere and how it changed with time. Supplied with the CERES data, they then combined it with estimates of oceanic heat content as recorded by three separate sensors. Their findings showed that both satellite and physical measurements of the ocean’s energy agreed with one another once observational uncertainties were added to the equation. Their work was summarized in a NASA-led study published January 22 in the journal Nature Geosciences,

“One of the things we wanted to do was a more rigorous analysis of the uncertainties. When we did that, we found the conclusion of missing energy in the system isn’t really supported by the data.” said Loeb. “Our data shows that Earth has been accumulating heat in the ocean at a rate of half a watt per square meter (10.8 square feet), with no sign of a decline. This extra energy will eventually find its way back into the atmosphere and increase temperatures on Earth.”

For the most part, scientists concur that around 90% of extra heat created by the greenhouse gas effect is being stored in Earth’s oceans. If it follows the laws of thermodynamics and is released back into the atmosphere, “a half-watt per square meter accumulation of heat could increase global temperatures by 0.3 or more degrees centigrade or 0.54 degree Fahrenheit”. As Loeb explained, these observations show the need to employ several different measuring systems over time and the findings underline the imperative need to continually update how Earth’s energy flows are recorded.

The newly published work came from the science team at the National Center for Atmospheric Research and other authors of the paper are from the University of Hawaii, the Pacific Marine Environmental Laboratory in Seattle, the University of Reading United Kingdom and the University of Miami. Their study mapped inconsistencies between satellite information on Earth’s heat balance between the years of 2004 and 2009 and included information on the rate of oceanic heating taken from the upper 700 meters of the surface. They said the inconsistencies were evidence of “missing energy.”

Original Story Source: JPL News Release.

NASA’s New Eyes in the Sky

An artist's concept of NuSTAR in space. Image credit: NASA/JPL-Caltech/Orbital

On March 14, NASA will launch the Nuclear Spectroscopic Telescope Array or NuSTAR. This is the first time a telescope will focus on high energy X-rays, effectively opening up the sky for more sensitive study. The telescope will target black holes, supernova explosions, and will study the most extreme active galaxies. NuSTAR’s use of high-energy X-rays have an added bonus: it will be able to capture and compose the most detailed images ever taken in this end of the electromagnetic spectrum. 

NuSTAR’s eyes are two Wolter-I optic units; once in orbit each will ‘look’ at the same patch of sky. The Wolter-I mirror works by reflecting an X-ray twice, once off of an upper mirror shaped like a parabola and again off a lower mirror shaped like a hyperbola. The mirrors are nearly parallel to the direction of the incoming X-ray, reflecting most of the X-ray instead of absorbing it, but the slight angle allows for a very small collection area per surface. To get a full picture, mirrors of varying size are nested together.

Technicians work on NuSTAR this month at the Orbital Science Corporation in Dulles, Virginia. Image credit: NASA/JPL-Caltech/Orbital

Each of NuSTAR’s eyes, each unit, are made of 133 concentric shells of mirrors shaped from flexible glass like that found in laptop computer screens. This is an improvement over past missions like Chandra and XMM-Newton that both used high density materials such as Platinum, Iridium and Gold as mirror coatings. These materials achieve great reflectivity for low energy X-rays but can’t capture high energy X-rays.

Like human eyes, NuSTAR’s optical units are co-aligned to give the telescope a wider field of view and enable the capture of more sensitive images. These images will be made into detailed composites by scientists on the ground.

Also like human eyes, NuSTAR’s optical units need to be distanced from one another since X-ray telescopes require long focal lengths. In other words, the optics must be separated by several meters from the detectors. NuSTAR does this with a 33 foot (10 metre) long mast or boom between units.

Previous X-ray missions have accommodated these long focal lengths by launching fully deployed observatories on large rockets. NuSTAR won’t. It has a unique deployable mast that will extend once the payload is in orbit. This allows for a launch on the small Pegasus rocket. Undeployed, the telescope measures just 2 metres in length and one metre in diameter.

During its two-year primary mission, NuSTAR will map the celestial sky focussing on black holes, supernova remnants, and particle jets traveling near the speed of light. It will also look at the Sun. Observations of microflares could explain the temperature of the Sun’s corona. It will also search the Sun for evidence of a hypothesized dark matter particle to test a theory about dark matter.

NuSTAR's mast. Image credit: NASA/JPL-Caltech/Orbital

“NuSTAR will provide an unprecedented capability to discover and study some of the most exotic objects in the universe, from the corpses of exploded stars in the Milky Way to supermassive black holes residing in the hearts of distant galaxies,” said Lou Kaluzienski, NuSTAR program scientist at NASA Headquarters in Washington.

The telescope shipped from the Orbital Sciences Corporation in Dulles, Virginia to Vandenberg Air Force Base in California on January 27. There, it will be mated to its Pegasus launch vehicle on February 17. It will launch from underneath the L-1011 “Stargazer” aircraft on March 14 after taking off near the equator from Kwajalein Atoll in the Pacific.

Source: NASA

A Pegasus rocket launches from underneath a L-1011 "Stargazer" aircraft, just like NuSTAR will do in March. Image credit: NASA/JPL-Caltech/Orbital

Asteroid To Make Closest Approach Since 1975

Asteroid 433 Eros as seen by NASA's NEAR spacecraft on Feb. 29, 2000. (NASA/JPL/JHUAPL)

On Tuesday, January 31, asteroid 433 Eros will come closer to Earth than it has in 37 years, traveling across the night sky in the constellations Leo, Sextans and Hydra. At its closest pass of 16.6 million miles (26.7 million km) the relatively bright 21-mile (34-km) -wide asteroid will be visible with even modest backyard telescopes, approaching magnitude 8, possibly even 7. It hasn’t come this close since 1975, and won’t do so again until 2056!

433 Eros is an S-type asteroid, signifying a composition of magnesium silicates and iron. S-types make up about 17 percent of known asteroids and are some of the brightest, with albedos (reflectivity) in the range of 0.10 – 0.22. S-type asteroids are most common in the inner asteroid belt and, as in the case of Eros, can even pass within the orbit of Mars.

Occasionally Eros’ orbit brings it close enough to Earth that it can be spotted with amateur telescopes. 2012 will be one of those times.

Eros was discovered on August 13, 1898, by astronomers Carl Gustav Witt in Berlin and Auguste Charlois in Nice. When Eros’ orbit was calculated it was seen to be an elongated oval that brought it within the orbit of Mars. This allowed for good observations of the bright asteroid, and eventually led to more accurate estimates of the distance from Earth to the Sun.

In February 2000 NASA’s NEAR Shoemaker spacecraft approached Eros, established orbit and made a soft landing on its surface, the first mission ever to do so. While in orbit NEAR took over 160,000 images of Eros’ surface, identifying over 100,000 craters, a million house-sized boulders (give or take a few) and helped researchers conclude that the cashew-shaped Eros is a solid object rather than a “rubble pile” held together by gravity.

View NEAR images of Eros’ surface.

Studying pristine objects like Eros gives insight into the earliest days of our solar system, and also allows scientists to better understand asteroid compositions… which is invaluable information when deciding how best to avoid any potential future impacts.

Orbit of 433 Eros for Jan. 31, 2012

Although Eros will be making a “close” approach to Earth on Jan. 31/Feb. 1, there is no danger of a collision. It will still remain at a very respectable distance of about 16.6 million miles (26.7 million km), or 0.178 AU. This is over 80 times the distance of the much smaller 2005 YU55, which safely passed within a lunar orbit radius on November 8, 2011.

If you do want to try viewing 433 Eros as it passes, you can find a diagram charting its pathfrom Sky and Telescope here. According to the Sydney Observatory’s website “the coordinates on 31 January (from the BAA 2012 Handbook) are 10 hours 33 minutes 19.0 seconds RA and -4° 48’ 23” declination. On 10 February the RA is 10 hours 20 minutes 27.6 seconds and the declination is -14° 38’ 49 seconds.”

Also there’s an updated chart on Heavens Above showing Eros’ current position.

Eros should remain visible up until Feb. 10.

Thanks to Skyscrapers, Inc., for a report on 433 Eros by Glenn Chaple. Skyscrapers, Inc. is an amateur astronomy society in Rhode Island that operates the Seagrave Observatory, whose centerpiece is a beautiful 8 1/4″ Alvan Clark telescope built in 1878. I saw Halley’s Comet through that telescope in 1986 and have been hooked on astronomy ever since.