Astronomy

Is the object a pulsar

Is the object a pulsar


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We have a star having 1.8 solar mass. Justify any four means (measurable/ observed properties) by which you can identify that the object is a Pulsar and not a white dwarf or a Black Hole.

So one obvious property would be the mass. Since mass > 1.4 solar mass, we can say it is not a white dwarf.

Also the mass is less than 3 solar mass, hence its not a black hole (I'm speaking loosely over here).

Also from periodic radiation patterns, we can say that the object might be a pulsar.

I need help with 2 other means to categorize this object.


  1. As you said, the mass range of the object indicates that it could be a neutron star, rather than a black hole.

  2. But also the density of the object is a clue. The density of a neutron star is much higher than that of a stable white dwarf.

  3. Extremely regular electromagnetic pulses have to be observed. Known pulsars have a pulse period between 1.4 ms and 8.5 seconds.

  4. The wavelength of the pulses is in the radio range.

  5. Pulsars slow down gradually, at a known rate, so you can measure how the pulse period evolves over time, and check that is compatible with the slow-down rate of a pulsar.

Adapted from this page


Pulsar

Pulsars are born in collapsing core supernova explosions. The rotation rate of the core-collapse increases enormously through conservation of angular momentum, and new-born pulsars typically spin at more than 60 times a second (60 Hz).

pulsar
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pulsar, in astronomy, a neutron star that emits brief, sharp pulses of energy instead of the steady radiation associated with other natural sources.

Pulsar Timing Method
Pulsar Timing is the method that was used in 1992 by Aleksander Wolszczan and Dale Frail to detect the first confirmed exoplanets. These exoplanets orbit a pulsar, which is a rapidly rotating neutron star. A neutron star is the extremely dense remnant of a star that exploded as a supernova.

is a rapidly rotating neutron star that sends out streams of electrons at nearly the speed of light along their magnetic poles.

s are thought to be rapidly spinning neutron stars, extremely dense stars composed almost entirely of neutrons and having a diameter of only 20 km (12 miles) or less. A neutron star is formed when the core of a violently exploding star called a supernova collapses inward and becomes compressed together.

Why don't all neutron stars become

s? (Advanced)
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s were quickly matched with the hypothetical neutron stars predicted in the 1930s.

is jointly powered by its magnetic field and its spin.

s and the Discovery of Neutron Stars
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P. F. Wang1,2,5, J. L. Han1,4,5, L. Han3, J. H. Zhang2,3, J. Q. Li2,3, C. Wang1,5, J. Han1, T. Wang1,4 and X. Y. Gao1,5 .

with a binary companion, often a white dwarf or neutron star.

s are rotating neutron stars that generate regular electromagnetic (EM) pulses at their spin rate. They were first discovered in the radio region of the EM spectrum by Jocelyn Bell and Anthony Hewish in 1967 [1].

emits two very high-energy beams into space, concentrated along its magnetic axis (the magnetic field is around one trillion (1,000,000,000,000) times that of the Earth's).

s based on their high energy gamma rays alone.

locations within the Terragen Sphere
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The first neutron stars to be detected were observed by radio telescopes as regularly repeating pulses of radio light with periods of about 1 second. These objects are called

s, and they happen to be the neutron stars oriented such that the Earth lies in the path of their lighthouse beam.

in 1967. At the time, she was a graduate student at Cambridge University. She was working with her advisor, Dr. Anthony Hewish, to make radio observations of the universe.

s
In the late 1960's astronomers discovered radio sources that pulsated very regularly with periods of just fractions of a second to a few seconds. The periods are extremely regular---only the ultra-high precision of atomic clocks can show a very slight lengthening in the period.

s are rapidly rotating neutron stars that emit radio waves in beams from their magnetic poles. The magnetic poles are not aligned with the rotation axis, as illustrated below. Thus, the radio beam sweeps around as the neutron star rotates, a thousand times every second.

A neutron star that rotates very fast, sending out "pulses" of radiation.
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- a type of neutron star that emits radiation in narrow beams a little like a lighthouse. For more information see neutron stars on the Weird Stars page.

A rotating neutron star whose radiation is observed as regular pulses.
Red giant A post-main sequence star of modest mass (a few solar masses or less) with an extended, relatively cool atmosphere.
Solar mass A mass equal to that of the Sun -- 2 x 1030 kg or about 330,000 Earth masses.

a rapidly rotating neutron star that bathes Earth in regular pulses of electromagnetic radiation.
quasar the highly energetic core of a young galaxy thought to be powered by a supermassive black hole short for quasi-stellar object.

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Regularly pulsating radio sources, with periods of order seconds or less. They are actually fastly neutron stars with a hot spot, which emits radiation in a cone as the star rotates, and are observable if Earth and our solar system happens lie within the cone.
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s: Spinning neutron stars that sling 'lighthouse beams' of radio waves around as they rotate.
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s have amazingly regular periods, which range from days to thousandths of seconds.

A spinning neutron star that emits energy along its gravitational axis. This energy is received as pulses as the star rotates. Discovered by Dame Jocelyn Bell and Anthony Hewish in the late 1960s.
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Or neutron star. A star of more than 1.3 but less than 3 so ar masses which has exhausted its nuclear fuel and has collapsed into a mass of degenerate neutrons.
Quasar (QSO)Quasi-stellar object. Highly red-shifted star-like objects of considerable controversy.

: A highly magnetized, rapidly rotating neutron star that emits beams of radiation along misaligned magnetic axis.

A source of short, precisely times radio bursts believed to be spinning neutron stars.
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spins (analogous to sweeping search-light beams).

s: A celestial object, thought to be a rapidly rotating neutron star, that emits regular pulses of radio waves and other electromagnetic radiation at rates of up to one thousand pulses per second.
Q .

- A rotating neutron star that showers earth with regular pulses of electromagnetic radiation.
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Quadrillion - a number represented in the U.S. with a 1 followed by 15 zeros, in the U.K., 1 followed by 24 zeros.

s may be observed at visible and shorter wavelengths.
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- A rotating neutron star with beams of radiation emerging from its magnetic poles. When the beams sweep past the Earth, we see "pulses" of radiation
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. See neutron star
Pythagoras, theorem of -- A proved assertion in geometry, that in a right-angled triangle which has sides of length (a, b, c), if c is the long side facing the right angle, then a2 + b2 = c2 .

(a) A fast-spinning neutron star that emits radiation toward Earth every-time it rotates. [C95]
(b) Neutron stars that spin rapidly and have strong magnetic fields, which produce electromagnetic radiation. (See Neutron Star) [LB90] .

s, pulsating radio sources with highly repeatable pulsation periods, are neutron stars of radius about 10 km and rotation period about 1 second. Their magnetic axis spins and beams radio waves, in a pattern similar to a lighthouse beam.

s are believed to vector the radio emissions so that if Earth lies in the line of sight they appear like a lighthouse (when seen by a radio telescope, that is).
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s are highly magnetized, rotating neutron stars that emit a beam of electromagnetic radiation. The observed periods of their pulses range from 1.4 milliseconds to 8.5 seconds.
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s are also called Neutron stars.

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pulsating variable star A star whose luminosity varies in a predictable, periodic way.

produces two powerful beams of radiation. These beams arise due to the intense magnetic field possessed by neutron stars, ∼ 108 T.

Originally, short for "pulsating radio star".
magnetic neutron stars, signal their presence to us by
radiation.

, they will cause slight anomalies in the timing of its observed radio pulses.

- (n.)
A rapidly rotating object, now known to be a neutron star, an extremely dense collapsed star where the electrons have been forced into the protons. The object is thus made up mainly of neutrons and a few kilometers in diameter.

sweeps past the Earth in a manner similar to the flash of light from a lighthouse beam.

s have periods as short as between one and two milliseconds and their periods are very constant.

s were dubbed LGMs. LGM stands for Little Green Men.
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(aka neutron star) is also a strong emitter of electromagnetic radiation that ranges from radio waves to gamma rays, and at X-ray and gamma energies above 30 Kev (Kilo Electron volt).

, discovered by R.A. Hulse and J.H. Taylor in 1974
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It's diameter can vary but is usually between 1,000 and 100,000 miles

at spaced intervals of several seconds or less .

A neutron star (burnt-out star) that emits radio waves which pulse on and off.
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s? Believe it or not, at first they did think the signals were from extraterrestrials due to the very precise nature of the pulses, but later trashed this idea when they discovered a wide range of pulse periods (the time between each pulse) located in many different directions in the sky.

s are neutron stars (NS) which have a mass of about 1.

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in the nebula marks the neutron-star corpse of the exploded star.

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West Virginia Student Discovers New Pulsar

A West Virginia high-school student has discovered a new pulsar, using data from the giant Robert C. Byrd Green Bank Telescope (GBT).

Shay Bloxton, 15, a participant in a project in which students analyze data from the radio telescope, spotted evidence of the pulsar on October 15. Bloxton, along with NRAO astronomers observed the object again one month later. The new observation confirmed that the object is a pulsar, a rotating, superdense neutron star. Bloxton is a sophomore at Nicholas County High School in Summersville, West Virginia.


Shay Bloxton
CREDIT: NRAO/AUI/NSF

"I was very excited when I found out I had actually made a discovery," Bloxton said. She went to Green Bank in November to participate in the follow-up observation. She termed that visit "a great experience."

"It also helped me learn a lot about how observations with the GBT are actually done," she added.

The project in which she participated, called the Pulsar Search Collaboratory (PSC), is a joint project of the National Radio Astronomy Observatory (NRAO) and West Virginia University, funded by a grant from the National Science Foundation.

Pulsars are known for their lighthouse-like beams of radio waves that sweep through space as the neutron star rotates, creating a pulse as the beam sweeps by the Earth. First discovered in 1967, pulsars serve as valuable natural "laboratories" for physicists studying exotic states of matter, quantum mechanics and General Relativity. The GBT, dedicated in 2000, has become one of the world's leading tools for discovering and studying pulsars.

The PSC, led by NRAO Education Officer Sue Ann Heatherly and Project Director Rachel Rosen, 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 1500 hours of observing with the GBT. The 120 terabytes of data were produced by 70,000 individual pointings of the giant, 17-million-pound telescope. Some 300 hours of the observing data were reserved for analysis by student teams.

The student teams use analysis software to reveal evidence of pulsars. Each portion of the data is analyzed by multiple teams. In addition to learning to use the analysis software, the student teams also must learn to recognize man-made radio interference that contaminates the data. The project will continue through 2011. Teachers interested in participating in the program can learn more at this link.

For Bloxton, the pulsar discovery may be only her first in a scientific career. "Participating in the PSC has definitely encouraged me to pursue my dream of being an astrophysicist," she said, adding that she hopes to attend West Virginia University to study astrophysics.

Late last year, another West Virginia student, from South Harrison High School, Lucas Bolyard, discovered a pulsar-like object called a rotating radio transient. His discovery also came through participation in the PSC.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.
Copyright © 2009 Associated Universities, Inc.


Pinpointing the Distance to a Pulsar

Astronomers have used the accuracy of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. The object, called PSR B0656+14, was previously thought to be up to 2,500 light-years away but it was at the same location in the sky as a supernova remnant which is only 1,000 light years away. This was thought to be a coincidence, but the new measurement from the VLBA pegs the pulsar at 950 light years away the same distance as the remnant – they were both created by the same supernova blast.

Location, location, and location. The old real-estate adage about what’s really important proved applicable to astrophysics as astronomers used the sharp radio “vision” of the National Science Foundation’s Very Long Baseline Array (VLBA) to pinpoint the distance to a pulsar. Their accurate distance measurement then resolved a dispute over the pulsar’s birthplace, allowed the astronomers to determine the size of its neutron star and possibly solve a mystery about cosmic rays.

“Getting an accurate distance to this pulsar gave us a real bonanza,” said Walter Brisken, of the National Radio Astronomy Observatory (NRAO) in Socorro, NM.

The pulsar, called PSR B0656+14, is in the constellation Gemini, and appears to be near the center of a circular supernova remnant that straddles Gemini and its neighboring constellation, Monoceros, and is thus called the Monogem Ring. Since pulsars are superdense, spinning neutron stars left over when a massive star explodes as a supernova, it was logical to assume that the Monogem Ring, the shell of debris from a supernova explosion, was the remnant of the blast that created the pulsar.

However, astronomers using indirect methods of determining the distance to the pulsar had concluded that it was nearly 2500 light-years from Earth. On the other hand, the supernova remnant was determined to be only about 1000 light-years from Earth. It seemed unlikely that the two were related, but instead appeared nearby in the sky purely by a chance juxtaposition.

Brisken and his colleagues used the VLBA to make precise measurements of the sky position of PSR B0656+14 from 2000 to 2002. They were able to detect the slight offset in the object’s apparent position when viewed from opposite sides of Earth’s orbit around the Sun. This effect, called parallax, provides a direct measurement of distance.

“Our measurements showed that the pulsar is about 950 light-years from Earth, essentially the same distance as the supernova remnant,” said Steve Thorsett, of the University of California, Santa Cruz. “That means that the two almost certainly were created by the same supernova blast,” he added.

With that problem solved. the astronomers then turned to studying the pulsar’s neutron star itself. Using a variety of data from different telescopes and armed with the new distance measurement, they determined that the neutron star is between 16 and 25 miles in diameter. In such a small size, it packs a mass roughly equal to that of the Sun.

The next result of learning the pulsar’s actual distance was to provide a possible answer to a longstanding question about cosmic rays. Cosmic rays are subatomic particles or atomic nuclei accelerated to nearly the speed of light. Shock waves in supernova remnants are thought to be responsible for accelerating many of these particles.

Scientists can measure the energy of cosmic rays, and had noted an excess of such rays in a specific energy range. Some researchers had suggested that the excess could come from a single supernova remnant about 1000 light-years away whose supernova explosion was about 100,000 years ago. The principal difficulty with this suggestion was that there was no accepted candidate for such a source.

“Our measurement now puts PSR B0656+14 and the Monogem Ring at exactly the right place and at exactly the right age to be the source of this excess of cosmic rays,” Brisken said.

With the ability of the VLBA, one of the telescopes of the NRAO, to make extremely precise position measurements, the astronomers expect to improve the accuracy of their distance determination even more.

“This pulsar is becoming a fascinating laboratory for studying astrophysics and nuclear physics,” Thorsett said.

In addition to Brisken and Thorsett, the team of astronomers includes Aaron Golden of the National University of Ireland, Robert Benjamin of the University of Wisconsin, and Miller Goss of NRAO. The scientists are reporting their results in papers appearing in the Astrophysical Journal Letters in August.

The VLBA is a continent-wide system of ten radio- telescope antennas, ranging from Hawaii in the west to the U.S. Virgin Islands in the east, providing the greatest resolving power, or ability to see fine detail, in astronomy. Dedicated in 1993, the VLBA is operated from the NRAO’s Array Operations Center in Socorro, New Mexico.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.


NRAO: National Radio Astronomy Observatory

In the constellation of Ophiuchus, above the disk of our Milky Way Galaxy, there lurks a stellar corpse spinning 30 times per second -- an exotic star known as a radio pulsar. This object was unknown until it was discovered last week by three high school students. These students are part of the Pulsar Search Collaboratory (PSC) project, run by the National Radio Astronomy Observatory (NRAO) in Green Bank, WV, and West Virginia University (WVU).


Alexander Snider and Hannah Mabry in GBT Control Room,
Casey Thompson on-screen, during confirmation observation.
CREDIT: NRAO/AUI/NSF

The pulsar, which may be a rare kind of neutron star called a recycled pulsar, was discovered independently by Virginia students Alexander Snider and Casey Thompson, on January 20, and a day later by Kentucky student Hannah Mabry. "Every day, I told myself, 'I have to find a pulsar. I better find a pulsar before this class ends,'" said Mabry.

When she actually made the discovery, she could barely contain her excitement. "I started screaming and jumping up and down."

Thompson was similarly expressive. "After three years of searching, I hadn't found a single thing," he said, "but when I did, I threw my hands up in the air and said, 'Yes!'."

Snider said, "It actually feels really neat to be the first person to ever see something like that. It's an uplifting feeling."

As part of the PSC, the students analyze real data from NRAO's Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. The students' teachers -- Debra Edwards of Sherando High School, Leah Lorton of James River High School, and Jennifer Carter of Rowan County Senior High School -- all introduced the PSC in their classes, and interested students formed teams to continue the work.

Even before the discovery, Mabry simply enjoyed the search. "It just feels like you're actually doing something," she said. "It's a good feeling."

Once the pulsar candidate was reported to NRAO, Project Director Rachel Rosen took a look and agreed with the young scientists. A followup observing session was scheduled on the GBT. Snider and Mabry traveled to West Virginia to assist in the follow-up observations, and Thompson joined online.

"Observing with the students is very exciting. It gives the students a chance to learn about radio telescopes and pulsar observing in a very hands-on way, and it is extra fun when we find a pulsar," said Rosen.

Snider, on the other hand, said, "I got very, very nervous. I expected when I went there that I would just be watching other people do things, and then I actually go to sit down at the controls. I definitely didn't want to mess something up."

Everything went well, and the observations confirmed that the students had found an exotic pulsar. "I learned more in the two hours in the control room than I would have in school the whole day," Mabry said.


Basics of a Pulsar
CREDIT: Bill Saxton, NRAO/AUI/NSF

Pulsars are spinning neutron stars that sling lighthouse beams of radio waves or light around as they spin. 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 -- as much as a supertanker.

The object that the students discovered is in a special class of pulsar that spins very fast - in this case, about 30 times per second, comparable to the speed of a kitchen blender.

"The big question we need to answer first is whether this is a young pulsar or a recycled pulsar," said Maura McLaughlin, an astronomer at WVU. "A pulsar spinning that fast is very interesting as it could be newly born or it could be a very old, recycled pulsar."

A recycled pulsar is one that was once in a binary system. Material from the companion star is deposited onto the pulsar, causing it to speed up, or be recycled. Mystery remains, however, about whether this pulsar has ever had a companion star.

If it did, "it may be that this pulsar had a massive companion that exploded in a supernova, disrupting its orbit," McLaughlin said. Astronomers and students will work together in the coming months to find answers to these questions.

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, led by NRAO Education Officer Sue Ann Heatherly and Project Director Rachel Rosen, 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, a giant, 17-million-pound telescope.

Some 300 hours of observing data were reserved for analysis by student teams. Thompson, Snider, and Mabry have been working with about 170 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 students' collective judgment sifts the pulsars from the noise.

All three students had analyzed thousands of data plots before coming upon this one. Casey Thompson, who has been with the PSC for three years, has analyzed more than 30,000 plots.

"Sometimes I just stop and think about the fact that I'm looking at data from space," Thompson said. "It's really special to me."

In addition to this discovery, two other astronomical objects have been discovered by students. In 2009, Shay Bloxton of Summersville, WV, discovered a pulsar that spins once every four seconds, and Lucas Bolyard of Clarksburg, WV, discovered a rapidly rotating radio transient, which astronomers believe is a pulsar that emits radio waves in bursts.

Those involved in the PSC hope that being a part of astronomy will give students an appreciation for science. Maybe the project will even produce some of the next generation of astronomers. Snider, surely, has been inspired.

"The PSC changed my career path," confessed Thompson. "I'm going to study astrophysics."

Snider is pleased with the idea of contributing to scientific knowledge. "I hope that astronomers at Green Bank and around the world can learn something from the discovery," he said.

Mabry is simply awed. "We've actually been able to experience something," she said.

The PSC will continue through 2011. 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.
Copyright © 2009 Associated Universities, Inc.


Astronomers Find “Cannonball Pulsar” Speeding Through Space

Astronomers using the National Science Foundation’s Karl G. Jansky Very Large Array (VLA) have found a pulsar speeding away from its presumed birthplace at nearly 700 miles per second, with its trail pointing directly back at the center of a shell of debris from the supernova explosion that created it. The discovery is providing important insights into how pulsars — superdense neutron stars left over after a massive star explodes — can get a “kick” of speed from the explosion.

“This pulsar has completely escaped the remnant of debris from the supernova explosion,” said Frank Schinzel, of the National Radio Astronomy Observatory (NRAO). “It’s very rare for a pulsar to get enough of a kick for us to see this,” he added.

The pulsar, dubbed PSR J0002+6216, about 6,500 light-years from Earth, was discovered in 2017 by a citizen-science project called [email protected] That project uses computer time donated by volunteers to analyze data from NASA’s Fermi Gamma-ray Space Telescope. So far, using more than 10,000 years of computing time, the project has discovered a total of 23 pulsars.

Radio observations with the VLA clearly show the pulsar outside the supernova remnant, with a tail of shocked particles and magnetic energy some 13 light-years long behind it. The tail points back toward the center of the supernova remnant.

“Measuring the pulsar’s motion and tracing it backwards shows that it was born at the center of the remnant, where the supernova explosion occurred,” said Matthew Kerr, of the Naval Research Laboratory. The pulsar now is 53 light-years from the remnant’s center.

“The explosion debris in the supernova remnant originally expanded faster than the pulsar’s motion,” said Dale Frail, of NRAO. “However, the debris was slowed by its encounter with the tenuous material in interstellar space, so the pulsar was able to catch up and overtake it,” he added.

The astronomers said that the pulsar apparently caught up with the shell about 5,000 years after the explosion. The system now is seen about 10,000 years after the explosion.

The pulsar’s speed of nearly 700 miles per second is unusual, the scientists said, with the average pulsar speed only about 150 miles per second. “This pulsar is moving fast enough that it eventually will escape our Milky Way Galaxy,” Frail said.

Astronomers have long known that pulsars get a kick when born in supernova explosions, but still are unsure how that happens.

“Numerous mechanisms for producing the kick have been proposed. What we see in PSR J0002+6216 supports the idea that hydrodynamic instabilities in the supernova explosion are responsible for the high velocity of this pulsar,” Frail said.

“We have more work to do to fully understand what’s going on with this pulsar, and it’s providing an excellent opportunity to improve our knowledge of supernova explosions and pulsars,” Schinzel said.

Schinzel, Kerr, and Frail worked with Urvashi Rau and Sanjay Bhatnagar, both of NRAO. The scientists are reporting their results at the High Energy Astrophysics Division meeting of the American Astronomical Society in Monterey, California, and have submitted a paper to the Astrophysical Journal Letters.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

The Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership managed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Fermi was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States.

[email protected] is a World Year of Physics 2005 and an International Year of Astronomy 2009 project. It is supported by the American Physical Society (APS), the US National Science Foundation (NSF), the Max Planck Society (MPG), and a number of international organizations.


Messier 82 Galaxy Harbors Mysterious, Extremely Bright Pulsar

An international team of astronomers, led Dr Matteo Bachetti of the University of Toulouse in France, has detected what they say is the most powerful pulsar ever spotted, with the energy of about 10 million suns.

A rare and mighty pulsar (magenta) can be seen at the center of Messier 82 in this image. Image credit: NASA / JPL-Caltech / SAO / NOAO.

Pulsars are dense stellar remnants left over from supernova explosions. They are typically between one and two times the mass of our Sun.

The newly-discovered object falls in that same range but shines about 100 times brighter than theory suggests something of its mass should be able to.

It is located in a nearby galaxy called Messier 82 (also known as NGC 3034, Cigar Galaxy or M82), about 12 million light-years away.

“This compact little stellar remnant is a real powerhouse. We’ve never seen anything quite like it. We all thought an object with that much energy had to be a black hole,” Prof Fiona Harrison from California Institute of Technology, Pasadena, a co-author of the paper published in the journal Nature.

Dr Bachetti, Prof Harrison and their colleagues identified the pulsar in the Messier 82’s nuclear region through NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR), a pair of orbiting telescopes that detect high-energy X-rays from far-off galaxies. They detected pulsations with an average period of 1.37 seconds and a 2.5-day sinusoidal modulation.

The exceptional brightness of this object classifies it as an ultraluminous X-ray (ULX) source – an object so bright that it defies any known process of stellar radiation.

Indeed, ULXs are scientific curiosities, and astronomers have proposed that such objects may be intermediate-mass black holes: not as small as stellar black holes, which have a mass five to 50 times that of our Sun, but not as big as supermassive black holes, which are 100,000 to 1 billion times as massive as the Sun.

“For decades everybody has thought these ultraluminous X-ray sources had to be black holes. But black holes don’t have a way to create this pulsing,” Prof Harrison said.

“But pulsars do. They are like giant magnets that emit radiation from their magnetic poles. As they rotate, an outside observer with an X-ray telescope, situated at the right angle, would see flashes of powerful light as the beam swept periodically across the observer’s field of view, like a lighthouse beacon.”

Prof Deepto Chakrabarty, head of the Astrophysics Division at Massachusetts Institute of Technology and a co-author of the discovery, added: “there are a number of ULX sources known, and until now, most people have assumed that they are black holes, and pretty massive. Now there may be other, similar ULX pulsars. And that would mean the whole picture that was being built up to try and explain this whole class of weird objects is wrong.”

With the pulsar and its location within Messier 82 identified, there are still many questions left to answer.

The object is many times higher than the Eddington limit, a basic physics guideline that sets an upper limit on the brightness that an object of a given mass should be able to achieve.

“This is the most extreme violation of that limit that we’ve ever seen. We have known that things can go above that by a small amount, but this blows that limit away,” said co-author Dr Dom Walton of California Institute of Technology, Pasadena.

M. Bachetti et al. 2014. An ultraluminous X-ray source powered by an accreting neutron star. Nature 514, 202–204 doi: 10.1038/nature13791


Probing the universality of free fall

This feature, known as the universality of free fall, lies at the foundation of Albert Einstein’s theory of general relativity. “Confirming it to this precision constitutes one of the most stringent tests of Einstein’s theory ever made - and the theory passes the test with flying colours”, says Guillaume Voisin. "Moreover, the results also provide very stringent constraints on alternative theories of gravity, which compete with Einstein&aposs general relativity to explain gravity and, for example, dark energy.”

The universality of free fall is a unique feature of gravity: Unlike all other interactions in nature, gravity attracts all material objects with the same acceleration. Galileo Galilei allegedly dropped several differently-sized weights from the leaning tower of Pisa to test this. Isaac Newton later considered this to be a fundamental principle of gravity, presenting it without a deeper explanation. The most precise test of the universality of free fall has, to date, been obtained by an especially designed satellite called Microscope (developed by the Centre Nationale d&aposÉtudes Spatiales, in France). The small proof masses within the satellite show identical accelerations in the gravitational field of the Earth to better than 1 part in 10 14 .


Is the object a pulsar - Astronomy




Eclipsing pulsar sheds light on Universe's densest objects
DR EMILY BALDWIN
ASTRONOMY NOW
Posted: 18 August 2010

Using NASA's Rossi X-ray Timing Explorer (RXTE), astronomers have discovered the first fast X-ray pulsar to be eclipsed by its companion star.

Pulsars are rapidly spinning neutron stars – the dense cores of massive stars that exploded as dramatic supernovae events at the end of their lives. They pack Sun-sized masses into a core that spans just 16-24 kilometres across, and spin hundreds of times per second.


Click here for larger image. J1749 is the first accreting millisecond pulsar to undergo eclipses. The pulsar and its companion star are separated by 1.22 million miles, or about five times the distance between Earth and the moon. Irradiated by the pulsar's intense X-rays, the star's outer layers puff up to make it about 20 percent larger than a star of its mass and age should be. Image: NASA/GSFC

RXTE detected an X-ray outburst from an object known as Swift J1749, which was originally detected by the Swift satellite in 2006 and found to be part of a binary system, feeding off gas from its stellar companion. The two stars orbit around each other every 8.8 hours and J1749 is spinning at a dizzy 518 times a second.

“Like many accreting binary systems, J1749 undergoes outbursts when instabilities in the accretion disc allow some of the gas to crash onto the neutron star,” says RXTE project scientist Tod Strohmayer. This is facilitated by the pulsar's intense magnetic fields that direct the infalling gas onto the star's magnetic poles.

During a week-long outburst in April of this year, RXTE recorded three periods where J1749’s X-ray emission appeared to disappear, corresponding to a 36 minute-long eclipse when the neutron star passes behind its companion. “This is the first time we’ve detected X-ray eclipses from a fast pulsar that is also accreting gas,” says Craig Markwardt at NASA’s Goddard Space Flight Center. “Using this information, we now know the size and mass of the companion star with unprecedented accuracy.”

The team determined that the normal star weighs around 70 percent of the Sun's mass, but that it is puffed up to some 20 percent larger than it should be for its mass and age. “We believe that the star’s surface is ‘puffed up’ by radiation from the pulsar, which is only about a million miles away from it,” says Markwardt. “This additional heating probably also makes the star’s surface especially disturbed and stormy.”

The pulsar's mass lies between 1.4 and 2.2 times the Sun's mass, but the team need one more piece of information to constrain this value. “We need to detect the normal star in the system with optical or infrared telescopes,” Strohmayer said. “Then we can measure its motion and extract the same information about the pulsar that the pulsar’s motion told us about the star.”

However, high-precision measurements of the X-ray pulses just before and after an eclipse – well within the capability of RXTE – may give the team the answer they are looking for. One consequence of relativity is that a signal (such as an X-ray pulse) experiences a slight timing delay when it passes very close to a massive object. Known as the Shapiro delay after its proposer Irwin Shaprio, this value is predicted as 21 microseconds for J1749. Although RXTE’s impressive timing resolution allows it to record changes seven times faster, with only three eclipses observed during the 2010 outburst it did not capture enough data to reveal a large delay. The data did set an upper limit on the star's mass however, for if the mass was greater than 2.2 times the Sun’s, RXTE would have seen the delay.

“We believe this is the first time anyone has set realistic limits for this effect at X-ray wavelengths outside of our Solar System,” says Markwardt. “The next time J1749 has an outburst, RXTE absolutely could measure its Shapiro delay.”

The results are reported in the 10 July issue of The Astrophysical Journal Letters.


Astronomers Discover the Brightest Pulsar to Date, NGC 5907 ULX

NGC 5907 ULX is the brightest pulsar ever observed. This image comprises X-ray emission data (blue/white) from ESA’s XMM-Newton space telescope and NASA’s Chandra X-ray Observatory, and optical data from the Sloan Digital Sky Survey (galaxy and foreground stars). The inset shows the X-ray pulsation of the spinning neutron star.

Using the European Space Agency’s XMM-Newton satellite and NASA’s NuSTAR, astronomers have discovered the brightest pulsar to date.

There’s a new record holder for brightest pulsar ever found — and astronomers are still trying to figure out how it can shine so brightly. It’s now part of a small group of mysterious bright pulsars that are challenging astronomers to rethink how pulsars accumulate, or accrete, material.

A pulsar is a spinning, magnetized neutron star that sweeps regular pulses of radiation in two symmetrical beams across the cosmos. If aligned well enough with Earth, these beams act like a lighthouse beacon — appearing to flash on and off as the pulsar rotates. Pulsars were previously massive stars that exploded in powerful supernovae, leaving behind these small, dense stellar corpses.

The brightest pulsar, as reported in the journal Science, is called NGC 5907 ULX. In one second, it emits the same amount of energy as our sun does in three-and-a-half years. The European Space Agency’s XMM-Newton satellite found the pulsar and, independently, NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission also detected the signal. This pulsar is 50 million light years away, which means its light dates back to a time before humans roamed Earth. It is also the farthest known neutron star.

“This object is really challenging our current understanding of the accretion process for high-luminosity pulsars,” said Gian Luca Israel, from INAF-Osservatorio Astronomica di Roma, Italy, lead author of the Science paper. “It is 1,000 times more luminous than the maximum thought possible for an accreting neutron star, so something else is needed in our models in order to account for the enormous amount of energy released by the object.”

The previous record holder for brightest pulsar was reported in October 2014. NuSTAR had identified M82 X-2, located about 12 million light-years away in the “Cigar Galaxy” galaxy Messier 82 (M82), as a pulsar rather than a black hole. The pulsar reported in Science, NGC 5907 ULX, is 10 times brighter.

Another extremely bright pulsar, the third brightest known, is called NGC 7793 P13. Using a combination of XMM-Newton and NuSTAR, one group of scientists reported the discovery in the Astrophysical Journal Letters, while another used XMM-Newton to report it in the Monthly Notices of the Royal Astronomical Society.

“They are brighter than what you would expect from an accreting black hole of 10 solar masses,” said Felix Fuerst, lead author of the Astrophysical Journal Letters study based at the European Space Astronomy Center in Madrid. Fuerst did this work while at Caltech in Pasadena, California.

How these objects are able to shine so brightly is a mystery. The leading theory is that these pulsars have strong, complex magnetic fields closer to their surfaces. A magnetic field would distort the flow of incoming material close to the neutron star. This would allow the neutron star to continue accreting material while still generating high levels of brightness.

It could be that many more ULXs are neutron stars, scientists say.

“These discoveries of ‘light,’ compact objects that shine so brightly, is revolutionizing the field,” Israel said.



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