Category: Astronomy

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Astronomers working with the Subaru Telescope have released these new images of a “fireworks display” in a near-infrared image of the Helix Nebula, showing comet-shaped knots within.

The Helix Nebula, NGC 7293, is not only one of the most interesting and beautiful planetary nebulae; it is also one of the closest nebulae to Earth, at a distance of only 710 light years away. The new image, taken with an infrared camera on the Subaru Telescope in Hawaii, shows tens of thousands of previously unseen comet-shaped knots inside the nebula. The sheer number of knots–more than have ever been seen before—looks like a massive fireworks display in space.

The Helix Nebula was the first planetary nebula in which knots were seen, and their presence may provide clues to what planetary material may survive at the end of a star’s life. Planetary nebulae are the final stages in the lives of low-mass stars, such as our Sun. As they reach the ends of their lives they throw off large amounts of material into space. Although the nebula looks like a fireworks display, the process of developing a nebula is neither explosive nor instantaneous; it takes place slowly, over a period of about 10,000 to 1,000,000 years. This gradual process creates these nebulae by exposing their inner cores, where nuclear burning once took place and from which bright ultraviolet radiation illuminates the ejected material.

Astronomers from the National Astronomical Observatory of Japan (NAOJ), from London, Manchester and Kent universities in the UK and from the University of Missouri in the US studied the emissions from hydrogen molecules in the infrared and found that knots are found throughout the entire nebula. Although these molecules are often destroyed by ultraviolet radiation in space, they have survived in these knots, shielded by dust and gas that can be seen in optical images. The comet-like shape of these knots results from the steady evaporation of gas from the knots, produced by the strong winds and ultraviolet radiation from the dying star in the center of the nebula.

Unlike previous optical images of the Helix Nebula knots, the infrared image shows thousands of clearly resolved knots, extending out from the central star at greater distances than previously observed. The extent of the cometary tails varies with the distance from the central star, just as Solar System comets have larger tails when they are closer to the Sun and when wind and radiation are stronger. “This research shows how the central star slowly destroys the knots and highlights the places where molecular and atomic material can be found in space,”says lead astronomer Dr. Mikako Matsuura, previously at NAOJ and now from University College London.

These images enable astronomers to estimate that there may be as many as 40,000 knots in the entire nebula, each of which are billions of kilometers/miles across. Their total mass may be as much as 30,000 Earths, or one-tenth the mass of our Sun. The origin of the knots is currently unknown.

This paper will be published in the Astrophysical Journal in August 2009

Final image caption: Previous optical image of the Helix Nebula, demonstrating diffuse gas surrounding a central star. The white box shows the area observed by the Subaru Telescope. Credit: NASA, NOAO, ESA, the Hubble Helix Nebula Team, M. Meixner [STScI], and T.A. Rector [NRAO]

Source: NAO of Japan

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For the first time, NASA’s Fermi Gamma-ray Space Telescope has spotted a new group of pulsars using only their gamma-ray emissions, in the absence of radio signals beamed to Earth. The 16 new objects are reported in this week’s edition of Science Express, in a study based out of the University of California in Santa Cruz.

A pulsar is a rapidly spinning neutron star, the dense core left behind after a supernova explosion. Most of the 1,800 known pulsars were found through their periodic radio emissions.

“These are the first pulsars ever detected by gamma rays alone, and already we’ve found 16,” said co-author Robert Johnson, a UC Santa Cruz physicist. “The existence of a large population of radio-quiet pulsars was suspected prior to this, but until Fermi was launched, only one radio-quiet pulsar was known, and it was first detected in x-rays.”

Of the 16 gamma-ray pulsars, 13 are associated with unidentified gamma-ray sources detected previously by the EGRET instrument on the Compton Gamma-ray Observatory. EGRET detected nearly 300 gamma-ray point sources, but was unable to detect pulsations from those sources, most of which have remained unidentified, said Pablo Saz Parkinson, also a SCIPP postdoctoral researcher and corresponding author of the paper.

“It’s been a longstanding question what could be powering those unidentified sources, and the new Fermi results tell us that a lot of them are pulsars,” Saz Parkinson said. “These findings are also giving us important clues about the mechanism of pulsar emissions.”

A pulsar emits narrow beams of radio waves from the magnetic poles of the neutron star, and the beams sweep around like a lighthouse beacon because the magnetic poles are not aligned with the star’s spin axis. If the radio beam misses the Earth, the pulsar cannot be detected by radio telescopes. Fermi’s ability to detect so many radio-quiet gamma-ray pulsars indicates that the gamma-rays are emitted in a beam that is wider and more fan-like than the radio beam.

The team identified the gamma-ray pulsars in data from Fermi’s Large Area Telescope (LAT). Marcus Ziegler, a postdoctoral researcher at UC Santa Cruz and corresponding author of the paper, said detection of gamma-ray pulsations from a typical source requires weeks or months of data from the LAT.

“From the faintest pulsar we studied, the LAT sees only two gamma-ray photons a day,” Ziegler said.

The very intense magnetic and electric fields of a pulsar accelerate charged particles to nearly the speed of light, and these particles are ultimately responsible for the gamma-ray emissions.

Because the rotation of the star powers the emissions, isolated pulsars slow down as they age and lose energy. But a binary companion star can feed material to a pulsar and spin it up to a rotation rate of 100 to 1,000 times a second. These are called millisecond pulsars, and Fermi scientists detected gamma-ray pulsations from eight millisecond pulsars that were previously discovered at radio wavelengths. Those results are reported in a second study also published in the July 2 edition of Science Express.

“Fermi has truly unprecedented power for discovering and studying gamma-ray pulsars,” said Paul Ray of the Naval Research Laboratory in Washington. “Since the demise of the Compton Gamma Ray Observatory a decade ago, we’ve wondered about the nature of unidentified gamma-ray sources it detected in our galaxy. These studies from Fermi lift the veil on many of them.”

Lead image caption: This all-sky map shows the positions of 16 new pulsars (yellow) and eight millisecond pulsars (magenta) studied using Fermi’s LAT. Credit: NASA/DOE/Fermi LAT Collaboration

Sources: Science and UC Santa Cruz, via Eurekalert.

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All you galactic hitchhikers take note: a new atlas of the inner regions of the Milky Way was released today, showing thousands of previously undiscovered dense knots of cold cosmic dust — the potential birthplaces of new stars. This new map of the home galaxy was made using observations from the APEX telescope in Chile, showing the Milky Way in submillitere wavelengths. “ATLASGAL gives us a new look at the Milky Way. Not only will it help us investigate how massive stars form, but it will also give us an overview of the larger-scale structure of our galaxy”, said Frederic Schuller from the Max Planck Institute for Radio Astronomy, leader of the ATLASGAL team.

So, grab your towels and let’s head out!

This is the largest map available of cold dust, and astronomers say it will provide an invaluable map for observations made with the forthcoming ALMA telescope, as well as the recently launched ESA Herschel space telescope.

The area of the new submillimeter map is approximately 95 square degrees, covering a very long and narrow strip along the galactic plane two degrees wide (four times the width of the full Moon) and over 40 degrees long. The 16,000 pixel-long map was made with the LABOCA submillimeter-wave camera on the ESO-operated APEX telescope. APEX is located at an altitude of 5100 m on the arid plateau of Chajnantor in the Chilean Andes — a site that allows optimal viewing in the submillimeter range. The Universe is relatively unexplored at submillimeter wavelengths, as extremely dry atmospheric conditions and advanced detector technology are required for such observations.

And click here to see an annotated pan of part of the galactic plane.

Highlights of the map include the center of the Milky Way, the nearby massive and dense cloud of molecular gas called Sagittarius B2, and a bubble of expanding gas called RCW120, where the interstellar medium around the bubble is collapsing and forming new stars.

“It’s exciting to get our first look at ATLASGAL, and we will be increasing the size of the map over the next year to cover all of the galactic plane visible from the APEX site on Chajnantor, as well as combining it with infrared observations to be made by the ESA Herschel Space Observatory. We look forward to new discoveries made with these maps, which will also serve as a guide for future observations with ALMA”, said Leonardo Testi from ESO, who is a member of the ATLASGAL team and the European Project Scientist for the ALMA project.

The interstellar medium — the material between the stars — is composed of gas and grains of cosmic dust, rather like fine sand or soot. However, the gas is mostly hydrogen and relatively difficult to detect, so astronomers often search for these dense regions by looking for the faint heat glow of the cosmic dust grains.
Submillimetre light allows astronomers to see these dust clouds shining, even though they obscure our view of the Universe at visible light wavelengths.

The newly released map also reveals thousands of dense dust clumps, many never seen before, which mark the future birthplaces of massive stars. The clumps are typically a couple of light-years in size, and have masses of between ten and a few thousand times the mass of our Sun. In addition, ATLASGAL has captured images of beautiful filamentary structures and bubbles in the interstellar medium, blown by supernovae and the winds of bright stars.

Source: ESO

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Let’s compare and contrast the two most different planets in the Solar System, Mercury and Jupiter. Of course, you probably know that Mercury is the smallest planet in the Solar System while Jupiter is the largest planet in the Solar System.

First, let’s just take a look at the physical measurements of Jupiter and Mercury. The diameter of Mercury is 4,879.4 km, while the diameter of Jupiter is 142,984 km. In other words, Jupiter is 29.3 times bigger across than Mercury. In terms of volume, you could fit 24,462 Mercurys inside Jupiter. Jupiter even has 5,750 times more mass than Mercury.

Now let’s take a look at their composition. Mercury is a rocky terrestrial planet, with a high density. In fact, the liquid iron core of Mercury accounts for 42% of the planet, and this is surrounded by a mantle and crust of silica. Jupiter in comparison is a relatively less dense gas giant planet; it’s made up almost entirely of hydrogen and helium, with a few other trace elements.

Mercury orbits very close to the Sun, with an average orbital distance of 57.9 million kilometers. Because it orbits so close, Mercury completes an orbit around the Sun every 88 days. Jupiter, on the other hand, is located 778.5 million km from the Sun and takes 11.86 years to complete a single year.

Mercury has no moons or rings, while Jupiter has a faint set of rings and 63 named natural satellites so far.

It sounds like Jupiter and Mercury are different in every way, but there’s one big similarity. You can see them both with your own eyes. Jupiter is very bright and often very high in the sky. In fact, if you see a really bright star in the sky in the middle of the night, you’re probably seeing Jupiter, and not a star at all. Mercury is also possible to see with your own eyes. But since Mercury orbits so close to the Sun, you’ll only see it shortly after sunset or before sunrise until the Sun washes out the night sky.

We have written many stories about Mercury here on Universe Today. Here’s an article about a the discovery that Mercury’s core is liquid. And how Mercury is actually less like the Moon than previously believed.

If you’d like more information on Mercury, check out NASA’s Solar System Exploration Guide, and here’s a link to NASA’s MESSENGER Misson Page.

We have also recorded a whole episode of Astronomy Cast that’s just about planet Mercury. Listen to it here, Episode 49: Mercury.

Mercurio y Júpiter

Reference:
NASA