psr b1919 21

Five Famous Pulsars from the Past 50 Years

Early astronomers faced an obstacle: their technology. These great minds only had access to telescopes that revealed celestial bodies shining in visible light. Later, with the development of new detectors, scientists opened their eyes to other types of light like radio waves and X-rays. They realized cosmic objects look very different when viewed in these additional wavelengths. Pulsars — rapidly spinning stellar corpses that appear to pulse at us — are a perfect example.

The first pulsar was observed 50 years ago on August 6, 1967, using radio waves, but since then we have studied them in nearly all wavelengths of light, including X-rays and gamma rays.

Typical Pulsar

Most pulsars form when a star — between 8 and 20 times the mass of our sun — runs out of fuel and its core collapses into a super dense and compact object: a neutron star

These neutron stars are about the size of a city and can rotate slowly or quite quickly, spinning anywhere from once every few hours to hundreds of times per second. As they whirl, they emit beams of light that appear to blink at us from space.

First Pulsar

One day five decades ago, a graduate student at the University of Cambridge, England, named Jocelyn Bell was poring over the data from her radio telescope - 120 meters of paper recordings.

Image Credit: Sumit Sijher

She noticed some unusual markings, which she called “scruff,” indicating a mysterious object (simulated above) that flashed without fail every 1.33730 seconds. This was the very first pulsar discovered, known today as PSR B1919+21.

Best Known Pulsar

Before long, we realized pulsars were far more complicated than first meets the eye — they produce many kinds of light, not only radio waves. Take our galaxy’s Crab Nebula, just 6,500 light years away and somewhat of a local celebrity. It formed after a supernova explosion, which crushed the parent star’s core into a neutron star. 

The resulting pulsar, nestled inside the nebula that resulted from the supernova explosion, is among the most well-studied objects in our cosmos. It’s pictured above in X-ray light, but it shines across almost the entire electromagnetic spectrum, from radio waves to gamma rays.

Brightest Gamma-ray Pulsar

Speaking of gamma rays, in 2015 our Fermi Gamma-ray Space Telescope discovered the first pulsar beyond our own galaxy capable of producing such high-energy emissions. 

Located in the Tarantula Nebula 163,000 light-years away, PSR J0540-6919 gleams nearly 20 times brighter in gamma-rays than the pulsar embedded in the Crab Nebula.

Dual Personality Pulsar

No two pulsars are exactly alike, and in 2013 an especially fast-spinning one had an identity crisis. A fleet of orbiting X-ray telescopes, including our Swift and Chandra observatories, caught IGR J18245-2452 as it alternated between generating X-rays and radio waves. 

Scientists suspect these radical changes could be due to the rise and fall of gas streaming onto the pulsar from its companion star.

Transformer Pulsar

This just goes to show that pulsars are easily influenced by their surroundings. That same year, our Fermi Gamma Ray Space Telescope uncovered another pulsar, PSR J1023+0038, in the act of a major transformation — also under the influence of its nearby companion star. 

The radio beacon disappeared and the pulsar brightened fivefold in gamma rays, as if someone had flipped a switch to increase the energy of the system. 

NICER Mission

Our Neutron star Interior Composition Explorer (NICER) mission, launched this past June, will study pulsars like those above using X-ray measurements.

With NICER’s help, scientists will be able to gaze even deeper into the cores of these dense and mysterious entities.

For more information about NICER, visit https://www.nasa.gov/nicer

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The Little Green Men

The Little Green Man is 50 years old today!  On this day in 1967 astronomer Jocelyn Burnell Bell found an unusual object blinking in a dark corner of the sky in the constellation Vulpecula. With a period of 1.3373 seconds and a pulse width of 0.04 second it was the first radio pulsar discovered, although Bell and her Ph.D. advisor astronomer Antony Hewish had no idea what exactly they were seeing. Given the regularity of the signal, they briefly (and mostly jokingly) considered the possibility that they had stumbled upon evidence of extra-terrestrial intelligence, and dubbed it LGM1, for Little Green Men 1. According to Bell:

We did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission. It is an interesting problem - if one thinks one may have detected life elsewhere in the universe how does one announce the results responsibly? Who does one tell first?

Thomas Gold and Franco Pacini suggested that pulsars were in fact pulsating neutron stars, confirmed with the discovery of a second pulsar in the Crab Nebula. The next year in March 1968, The Daily Telegraph was first to publish the new word:

An entirely novel kind of star came to light on Aug. 6 last year and was referred to, by astronomers, as LGM (Little Green Men). Now it is thought to be a novel type between a white dwarf and a neutron [sic]. The name Pulsar is likely to be given to it. Dr. A. Hewish told me yesterday: “… I am sure that today every radio telescope is looking at the Pulsars.”

The word itself was a combination of pulsating and star, a very literal and descriptive explanation of what scientists were seeing. Today that first pulsar is known variously as CP 1919, PSR B1919+21 and PSR J1921+2153.

Pulsars are so unique that NASA used them as intergalactic locators, drawing a map on the Pioneer plaques to allow extra-terrestrial intelligences to find planet Earth.

In 1974 Antony Hewish became the first astronomer to win a Nobel Prize in Physics, with a bit of controversy surrounding the award as Bell (who actually discovered the pulsar) was not co-awarded the prize.

All images used under CC 3.0 license.

Neutron Stars Are Weird!

There, we came right out and said it. They can’t help it; it’s just what happens when you have a star that’s heavier than our sun but as small as a city. Neutron stars give us access to crazy conditions that we can’t study directly on Earth.

Here are five facts about neutron stars that show sometimes they are stranger than science fiction!

1. Neutron stars start their lives with a bang

When a star bigger and more massive than our sun runs out of fuel at the end of its life, its core collapses while the outer layers are blown off in a supernova explosion. What is left behind depends on the mass of the original star. If it’s roughly 7 to 19 times the mass of our sun, we are left with a neutron star. If it started with more than 20 times the mass of our sun, it becomes a black hole.

2. Neutron stars contain the densest material that we can directly observe

While neutron stars’ dark cousins, black holes, might get all the attention, neutron stars are actually the densest material that we can directly observe. Black holes are hidden by their event horizon, so we can’t see what’s going on inside. However, neutron stars don’t have such shielding. To get an idea of how dense they are, one sugar cube of neutron star material would weigh about 1 trillion kilograms (or 1 billion tons) on Earth—about as much as a mountain. That is what happens when you cram a star with up to twice the mass of our sun into a sphere the diameter of a city.

3. Neutron stars can spin as fast as blender blades

Some neutron stars, called pulsars, emit streams of light that we see as flashes because the beams of light sweep in and out of our vision as the star rotates. The fastest known pulsar, named PSR J1748-2446ad, spins 43,000 times every minute. That’s twice as fast as the typical household blender! Over weeks, months or longer, pulsars pulse with more accuracy than an atomic clock, which excites astronomers about the possible applications of measuring the timing of these pulses.

4. Neutron stars are the strongest known magnets

Like many objects in space, including Earth, neutron stars have a magnetic field. While all known neutron stars have magnetic fields billions and trillions of times stronger than Earth’s, a type of neutron star known as a magnetar can have a magnetic field another thousand times stronger. These intense magnetic forces can cause starquakes on the surface of a magnetar, rupturing the star’s crust and producing brilliant flashes of gamma rays so powerful that they have been known to travel thousands of light-years across our Milky Way galaxy, causing measurable changes to Earth’s upper atmosphere.

5. Neutron stars’ pulses were originally thought to be possible alien signals

Beep. Beep. Beep. The discovery of pulsars began with a mystery in 1967 when astronomers picked up very regular radio flashes but couldn’t figure out what was causing them. The early researchers toyed briefly with the idea that it could be a signal from an alien civilization, an explanation that was discarded but lingered in their nickname for the original object—LGM-1, a nod to the “little green men” (it was later renamed PSR B1919+21). Of course, now scientists understand that pulsars are spinning neutron stars sending out light across a broad range of wavelengths that we detect as very regular pulses – but the first detections threw observers for a loop.

The Neutron star Interior Composition Explorer (NICER) payload that is soon heading to the International Space Station will give astronomers more insight into neutron stars—helping us determine what is under the surface. Also, onboard NICER, the Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) experiment will test the use of pulsars as navigation beacons in space.

Want to learn even more about Neutron Stars? Watch this…

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About that Alien Megastructure around  KIC 8462852…

Scientists shocked the world this week with the announcement of an unusual discovery by the Kepler program.   Tabetha Boyajian of Yale University led a team watching a star (KIC 8462852) around 1500 light years from Earth whose unusual light patterns defy current understanding.  Several hypotheses have been offered, including the possibility that indeed, a giant alien megastructure was found.  But it isn’t the first time scientists found unusual bodies deep in space.

In 1967 astronomer Jocelyn Burnell Bell found an unusual object blinking in a dark corner of the sky in the constellation Vulpecula. With a period of 1.3373 seconds and a pulse width of 0.04 second it was the first radio pulsar discovered, although Bell and her Ph.D. advisor astronomer Antony Hewish had no idea what exactly they were seeing. Given the regularity of the signal, they briefly (and mostly jokingly) considered the possibility that they had stumbled upon evidence of extra-terrestrial intelligence, and dubbed it LGM1, for Little Green Men 1. According to Bell:

We did not really believe that we had picked up signals from another civilization, but obviously the idea had crossed our minds and we had no proof that it was an entirely natural radio emission. It is an interesting problem - if one thinks one may have detected life elsewhere in the universe how does one announce the results responsibly? Who does one tell first?

Thomas Gold and Franco Pacini suggested that pulsars were in fact pulsating neutron stars, confirmed with the discovery of a second pulsar in the Crab Nebula. The next year in March 1968, The Daily Telegraph was first to publish the new word:

An entirely novel kind of star came to light on Aug. 6 last year and was referred to, by astronomers, as LGM (Little Green Men). Now it is thought to be a novel type between a white dwarf and a neutron [sic]. The name Pulsar is likely to be given to it. Dr. A. Hewish told me yesterday: “… I am sure that today every radio telescope is looking at the Pulsars.”

The word itself was a combination of pulsating and star, a very literal and descriptive explanation of what scientists were seeing. Today that first pulsar is known variously as CP 1919, PSR B1919+21 and PSR J1921+2153.

Pulsars are so unique that NASA used them as intergalactic locators, drawing a map on the Pioneer plaques to allow extra-terrestrial intelligences to find planet Earth.

In 1974 Antony Hewish became the first astronomer to win a Nobel Prize in Physics, with a bit of controversy surrounding the award as Bell (who actually discovered the pulsar) was not co-awarded the prize.

Perhaps Tabetha Boyajian has found the first concrete evidence of extraterrestrial life.  Let’s hope scientists can devote more resources to study this unusual star.

All images used under CC 3.0 license.