Stars Archives

January 2, 2015December 23, 2015 by Matt Williams

Rogue Star HIP 85605 on Collision Course with our Solar System, but Earthlings Need Not Worry

Collisions of neutron stars produce powerful gamma-ray bursts – and heavy elements like gold (Credit: Dana Berry, SkyWorks Digital, Inc.)

It’s known as HIP 85605, one of two stars that make up a binary in the Hercules constellation roughly 16 light years away. And if a recent research paper produced by Dr. Coryn Bailer-Jones of the Max Planck Institute for Astronomy in Heidelberg, Germany is correct, it is on a collision course with our Solar System.

Now for the good news: according to Bailer-Jones’ calculations, the star will pass by our Solar System at a distance of 0.04 parsecs, which is equivalent to 8,000 times the distance between the Earth and the Sun (8,000 AUs). In addition, this passage will not affect Earth or any other planet’s orbit around the Sun. And perhaps most importantly of all, none of it will be happening for another 240,000 to 470,000 years from now.

“Even though the galaxy contains very many stars,” Bailer-Jones told Universe Today via email, “the spaces between them are huge. So even over the (long) life of our galaxy so far, the probability of any two stars have actually collided — as opposed to just coming close — is extremely small.”

However, in astronomical terms, that still counts as a near-miss. In a universe that is 46 billion light years in any direction – and that’s just the observable part of it – an event that is expected to take place just 50 light days away is considered to be pretty close. And in the context of space and time, a quarter of a million to half a million years is the very near future.

The real concern is the effect that the passage of HIP 85605 could have on the Oort Cloud – the massive cloud of icy planetesimals that surrounds the Solar System. Given that it’s distance is between 20,000 and 50,000 AU from our Sun, HIP 85605 would actually move through the Oort cloud and cause serious disruption.

The layout of the solar system, including the Oort Cloud, on a logarithmic scale. Credit: NASA — *The layout of the Solar System, including the Oort Cloud, which lies 50,000 AU from our Sun. Credit: NASA*

Many of these planetesimals could be blown off into space, but others could be sent hurtling towards Earth. Assuming humanity is still around at this point in time, this could present a bit of an inconvenience, even if it is spread over the course of a million years.

As it stands, such “close encounters” between stars are quite rare. Stellar collisions usually only occur within binaries, where white dwarfs or neutron stars are concerned. “The exception to this is physically bound binary stars in a tight orbit,” said Bailer-Jones. “It can and does happen that one star expands during its evolution and will then interfere with the evolution of the other star. Neutron-neutron star pairs can even merge.”

But of course, on an astronomical timescale, stars passing each other by as they perform their cosmic dance is actually a pretty common occurrence. As part of Bailer-Jones larger study of over 50,000 stars within our galaxy, this “close encounter” is one of several predicted to take place in the coming years.

Of all of them, only HIP 85605 is expected to come within a single parsec between 240 and 470 thousand years from now. He also indicates with (90% confidence) that the last time such an encounter took place was 3.8 million years ago when gamma Microscopii – a G7 giant which has two and a half times the mass of our Sun – came within 0.35-1.34 pc of our system, which may have caused a large perturbation in the Oort cloud.

Chandra data (above, graph) on J0806 show that its X-rays vary with a period of 321.5 seconds, or slightly more than five minutes. This implies that the X-ray source is a binary star system where two white dwarf stars are orbiting each other (above, illustration) only 50,000 miles apart, making it one of the smallest known binary orbits in the Galaxy. According to Einstein's General Theory of Relativity, such a system should produce gravitational waves - ripples in space-time - that carry energy away from the system and cause the stars to move closer together. X-ray and optical observations indicate that the orbital period of this system is decreasing by 1.2 milliseconds every year, which means that the stars are moving closer at a rate of 2 feet per year. — *Tightly bound binary stars, like the ones illustrated here, sometimes result in stellar collisions. Credit: Chandra*

On his MPIA webpage, in the study’s FAQ section, Bailer-Jones claims that his research into stellar close encounters was motivated by a desire to study the potential impacts of astronomical phenomena on Earth, and is part of a larger program named “astroimpacts”.

“I am interested in the history of the Earth,” he says, “and astronomical phenomena have clearly played a role in this. But what role precisely, how significant, and what can we expect to happen in the future?” Whereas several studies have been conducted in the past, he feels that the methods – which include assuming a linear relative motion of stars – produces inaccurate results.”

In contrast, Bailer-Jones study relies on “more recent data or re-analyses of data to produce hopefully more accurate results, and then compensate more rigorously for the uncertainties in the data, so that I can attach probabilities to my statements.”

As a result of this, he predicts that HIP 85605 has a 90% chance of passing within a single parsec of our Sun in the next 240 to 470 thousands years. However, he also admits that if the astronomy is incorrect, the next closest encounter won’t be happening for another 1.3 million years, when a K7 dwarf known as GL 710 is predicted to pass within 0.10 – 0.44 parsecs.

Bailer-Jones also believes that the European Space Agency’s Gaia spacecraft will help make more accurate predictions in the future. By understanding and mapping the environment of the Milky Way Galaxy, measuring the gravitational potential and determining the velocity of stars, scientists will be able to see how their various orbits around the galaxy’s center could cause them to intersect.

Artistic impression of what Kepler-186f may look like. Image Credit: NASA Ames/SETI Institute/JPL-CalTech — *It is likely that passing stars have a system of exoplanets (like Kepler-186f pictured here), which would place them within a few parsecs of Earth. Image Credit: NASA Ames/SETI Institute/JPL-CalTech*

But perhaps the most interesting question explored on his webpage is the possibility of using stellar close encounters as a shortcut for exploring exoplanets. According to current cosmological models, the majority of stars within our galaxy are believed to host exoplanets.

So if a star is passing us at just a few parsecs (or even with a single parsec) why not hop on over and investigate its planets? Well, as Bailer-Jones indicates, that’s not really a practical idea: “Traveling to a star passing our solar system at a distance of around 1 pc with a relative speed of 30 km/s is no easier than traveling the the nearby stars (the nearest of which is just over 1 pc away). And we would have to wait 10s of thousands of years for the next encounter. If we can ever achieve interstellar travel, I don’t suppose it would take that long to achieve, so why wait?”

Darn. Still, if there’s one thing this phenomena and Bailer-Jones study reminds us, it is that in the course of dancing around the center of the Milky Way, stars are not fixed in a single point in space. Not only do they periodically move within reach of each other, they can also have an affect on life within them.

Alas, the timescale on which such things happen, not to mention the consequences they entail, are so large that people here on Earth need not worry. By the time HIP 85605 or GL 710 come within a parsec or two of us, we’ll either be long-since dead or too highly evolved to care!

*Update: According to a new study posted by Erick E. Mamajek and associates on arXiv, the passage of the recently-discovered low mass star W0720 (aka. “Scholtz Star”) – roughly 70,000 years ago and at a distance of 0.25 Parsecs from our Sun – was the closest encounter our Solar System has had with another star. They calculate the possibility that it would have penetrated the System’s Outer Oort Cloud at 98%. However, they also estimate that the impact it would have had on the flux of long-period comets was negligible, but that the passage also highlights how “dynamically important Oort Cloud perturbers may be lurking among nearby stars”.

Having read the study, Bailer-Jones claims on the updated FAQ section of his MPIA webpage that their analysis appears to be correct. Based on the assumption that the star was moving on a constant velocity relative to the Sun prior to the encounter, he agrees that the calculations on the distances and timing of the passage are valid. While his own study identified a possible closer encounter (Hip 85605), he reiterates that the data on this star is of poor quality. Meanwhile, another close encounter took place involving Hip 89825; but here, the approach distance is estimated to have been 0.02 Parsecs larger. Hence, W0720 can be said to have been the closest encounter with some degree of certainty at this time.

The study appeared on Feb. 16th at arXiv Astrophysics.

Further Reading: arXiv Astrophysics, Max Planck Institute of Astronomy

December 22, 2014December 23, 2015 by Jason Major

NASA’s NuSTAR Scans the Sun with X-ray Vision

The west limb of the Sun imaged by NuSTAR and SDO shows areas of high-energy x-rays above particularly active regions (NASA/JPL-Caltech/GSFC)

What if you had x-ray vision like Superman? Or if those funny-looking glasses they advertised in comic books in the 60s actually worked?* Then with those our Sun might look something like this, lighting up with brilliant flares of high-energy x-rays as seen by NASA’s super-sensitive NuSTAR Space Telescope (with a little help from SDO.)

The NuStar Space Telescope launched into Earth orbit by a Orbital Science Corp. Pegasus rocket, 2012. The Wolter telescope design images throughout a spectral range from 5 to 80 KeV. (Credit: NASA/Caltech-JPL) — The NuStar Space Telescope launched aboard a Orbital Sciences Pegasus rocket, on June 13, 2012. (Credit: NASA/Caltech-JPL)

Of course NASA’s orbiting NuSTAR x-ray telescope is not like a typical medical imaging system. Instead of looking for broken bones, NuSTAR (short for Nuclear Spectroscopic Telescope Array) is made to detect high-energy particles blasting across the Universe from exotic objects like supermassive black holes, pulsars, and supernovae.

But astronomers suggested turning NuSTAR’s gaze upon our own Sun to see what sorts of x-ray activity may be going on there.

“At first I thought the whole idea was crazy,” said Fiona Harrison, a Professor of Physics and Astronomy at Caltech and PI for the NuSTAR mission. “Why would we have the most sensitive high energy X-ray telescope ever built, designed to peer deep into the universe, look at something in our own back yard?”

As it turns out NuSTAR was able to reveal some very interesting features on the Sun, showing where the corona is being heated to very high temperatures. The image above shows NuSTAR’s first observations, overlaid onto data acquired by NASA’s Solar Dynamics Observatory.

NuSTAR data is shown in green and blue, revealing high-energy emission around – but not exactly aligned with – active regions on the Sun where solar plasma is being heated to more than 3 million degrees. The red represents ultraviolet light captured by SDO and shows material in the solar atmosphere at a slightly cooler 1 million degrees.

The west limb of the Sun imaged by NuSTAR and SDO shows areas of high-energy x-rays near active regions and coronal loops (NASA/JPL-Caltech/GSFC) — The NuSTAR data overlaid on the full disk SDO image, rotated so north on the Sun is up. (NASA/JPL-Caltech/GSFC)

Because the Sun isn’t terribly intense in high energy x-ray output it’s safe to observe it with NuSTAR — it’s not likely to burn out the telescope’s sensors. But what NuSTAR can detect may help astronomers determine the exact mechanisms behind the intense coronal heating that occurs in and above the Sun’s chromosphere. If so-called “nanoflares” — miniature and as-yet-invisible versions of solar flares — are responsible, for instance, NuSTAR might be able to catch them in action for the first time.

“NuSTAR will be exquisitely sensitive to the faintest X-ray activity happening in the solar atmosphere, and that includes possible nanoflares,” said David Smith, solar physicist and member of the NuSTAR team at the University of California, Santa Cruz.

In addition NuSTAR could potentially detect the presence of axions in the Sun’s core — hypothesized particles that may make up dark matter in the Universe.

NuSTAR may not be a “solar telescope” per se, but that won’t stop astronomers from using its unique abilities to learn more about the star we intimately share space with.

“NuSTAR will give us a unique look at the Sun, from the deepest to the highest parts of its atmosphere.”

– David Smith, solar physicist, University of California Santa Cruz

What Does It Mean To Be ‘Star Stuff’?

This Chandra image of the Tycho supernova remnant contains new evidence for what triggered the original supernova explosion. Credit: NASA/CXC/Chinese Academy of Sciences/F. Lu et al.

At one time or another, all science enthusiasts have heard the late Carl Sagan’s infamous words: “We are made of star stuff.” But what does that mean exactly? How could colossal balls of plasma, greedily burning away their nuclear fuel in faraway time and space, play any part in spawning the vast complexity of our Earthly world? How is it that “the nitrogen in our DNA, the calcium in our teeth, the iron in our blood, the carbon in our apple pies” could have been forged so offhandedly deep in the hearts of these massive stellar giants?

Unsurprisingly, the story is both elegant and profoundly awe-inspiring.

All stars come from humble beginnings: namely, a gigantic, rotating clump of gas and dust. Gravity drives the cloud to condense as it spins, swirling into an ever more tightly packed sphere of material. Eventually, the star-to-be becomes so dense and hot that molecules of hydrogen in its core collide and fuse into new molecules of helium. These nuclear reactions release powerful bursts of energy in the form of light. The gas shines brightly; a star is born.

The ultimate fate of our fledgling star depends on its mass. Smaller, lightweight stars burn though the hydrogen in their core more slowly than heavier stars, shining somewhat more dimly but living far longer lives. Over time, however, falling hydrogen levels at the center of the star cause fewer hydrogen fusion reactions; fewer hydrogen fusion reactions mean less energy, and therefore less outward pressure.

At a certain point, the star can no longer maintain the tension its core had been sustaining against the mass of its outer layers. Gravity tips the scale, and the outer layers begin to tumble inward on the core. But their collapse heats things up, increasing the core pressure and reversing the process once again. A new hydrogen burning shell is created just outside the core, reestablishing a buffer against the gravity of the star’s surface layers.

While the core continues conducting lower-energy helium fusion reactions, the force of the new hydrogen burning shell pushes on the star’s exterior, causing the outer layers to swell more and more. The star expands and cools into a red giant. Its outer layers will ultimately escape the pull of gravity altogether, floating off into space and leaving behind a small, dead core – a white dwarf.

Lower-mass stars like our sun eventually enter a swollen, red giant phase. Ultimately, its outer layers will be thrown off altogether, leaving nothing but a small white dwarf star. Image Credit: ESO/S. Steinhofel

Heavier stars also occasionally falter in the fight between pressure and gravity, creating new shells of atoms to fuse in the process; however, unlike smaller stars, their excess mass allows them to keep forming these layers. The result is a series of concentric spheres, each shell containing heavier elements than the one surrounding it. Hydrogen in the core gives rise to helium. Helium atoms fuse together to form carbon. Carbon combines with helium to create oxygen, which fuses into neon, then magnesium, then silicon… all the way across the periodic table to iron, where the chain ends. Such massive stars act like a furnace, driving these reactions by way of sheer available energy.

But this energy is a finite resource. Once the star’s core becomes a solid ball of iron, it can no longer fuse elements to create energy. As was the case for smaller stars, fewer energetic reactions in the core of heavyweight stars mean less outward pressure against the force of gravity. The outer layers of the star will then begin to collapse, hastening the pace of heavy element fusion and further reducing the amount of energy available to hold up those outer layers. Density increases exponentially in the shrinking core, jamming together protons and electrons so tightly that it becomes an entirely new entity: a neutron star.

At this point, the core cannot get any denser. The star’s massive outer shells – still tumbling inward and still chock-full of volatile elements – no longer have anywhere to go. They slam into the core like a speeding oil rig crashing into a brick wall, and erupt into a monstrous explosion: a supernova. The extraordinary energies generated during this blast finally allow the fusion of elements even heavier than iron, from cobalt all the way to uranium.

Periodic Table of Elements. Massive stars can fuse elements up to Iron (Fe), atomic number 26. Elements with atomic numbers 27 through 92 are produced in the aftermath of a massive star’s core collapse.

The energetic shock wave produced by the supernova moves out into the cosmos, disbursing heavy elements in its wake. These atoms can later be incorporated into planetary systems like our own. Given the right conditions – for instance, an appropriately stable star and a position within its Habitable Zone – these elements provide the building blocks for complex life.

Today, our everyday lives are made possible by these very atoms, forged long ago in the life and death throes of massive stars. Our ability to do anything at all – wake up from a deep sleep, enjoy a delicious meal, drive a car, write a sentence, add and subtract, solve a problem, call a friend, laugh, cry, sing, dance, run, jump, and play – is governed mostly by the behavior of tiny chains of hydrogen combined with heavier elements like carbon, nitrogen, oxygen, and phosphorus.

Other heavy elements are present in smaller quantities in the body, but are nonetheless just as vital to proper functioning. For instance, calcium, fluorine, magnesium, and silicon work alongside phosphorus to strengthen and grow our bones and teeth; ionized sodium, potassium, and chlorine play a vital role in maintaining the body’s fluid balance and electrical activity; and iron comprises the key portion of hemoglobin, the protein that equips our red blood cells with the ability to deliver the oxygen we inhale to the rest of our body.

So, the next time you are having a bad day, try this: close your eyes, take a deep breath, and contemplate the chain of events that connects your body and mind to a place billions of lightyears away, deep in the distant reaches of space and time. Recall that massive stars, many times larger than our sun, spent millions of years turning energy into matter, creating the atoms that make up every part of you, the Earth, and everyone you have ever known and loved.

We human beings are so small; and yet, the delicate dance of molecules made from this star stuff gives rise to a biology that enables us to ponder our wider Universe and how we came to exist at all. Carl Sagan himself explained it best: “Some part of our being knows this is where we came from. We long to return; and we can, because the cosmos is also within us. We’re made of star stuff. We are a way for the cosmos to know itself.”

December 9, 2014December 23, 2015 by Bob King

How Low Can You Go? Take the Great Square Challenge

Look high in the southern sky at nightfall to find the familiar giant square that forms part of the body of Pegasus the Flying Horse. The map shows the sky around 6:30 p.m. local time. Source: Stellarium

Cast your gaze up, up, up on the next dark, moonless night and stare into the Great Square of Pegasus. How many stars do you see? Zero? Two? Twenty? If you’d like to find out how dark your sky is, read on.

The Great Square, one of the fall sky’s best known star patterns, rides high in the south at nightfall in mid-December. It forms part of the larger figure of Pegasus the Winged Horse. For our purposes today, we’re going to concentrate on what’s inside the square.

Bounded by Alpheratz (officially belonging to adjacent Andromeda), Scheat, Markab and Algenib, the Great Square is about 15° on a side or one-and-a-half balled fists held at arm’s length.

At first glance, the space appears empty, but a closer look from all but the most light polluted skies will reveal a pair 4th magnitude stars in the upper right quadrant of the square. Fourth magnitude is about the viewing limit from a bright suburban location.

Astronomers use the magnitude scale to measure star and planet brightness. Each magnitude is 2.5 times brighter than the one below it. Aldebaran, which shines at 1st magnitude, is 2.5 times brighter than a 2nd magnitude star, which in turn is 2.5 times brighter than a 3rd magnitude star and so on.

Moonlight and especially light pollution reduce the number of stars we can see in the night sky. This specially prepared map shows slices of sky based on amateur astronomer and author John Bortle's Dark Sky Scale. Classes range from 1 (excellent with stars fainter than 7th magnitude visible) to 9 (inner city with a limiting magnitude of 4). Click for more detailed descriptions of each class and rate your own sky. Credit: International Dark Sky Association — Moonlight and especially light pollution reduce the number of stars we can see in the night sky. This specially prepared map shows slices of sky based on amateur astronomer and author John Bortle’s Dark Sky Scale. Classes range from 1 (excellent with stars fainter than 7th magnitude visible) to 9 (inner city with a limiting magnitude of 4). Click for more detailed descriptions of each class and rate your own sky. Credit: International Dark Sky Association

A first magnitude star is 2.5 x 2.5 x 2.5 x 2.5 x 2.5 (about 100) times brighter than a 6th magnitude star. The bigger the magnitude number, the fainter the star. From cities, you might see 3rd magnitude stars if you can block out stray lighting, but a dark country sky will deliver the Holy Grail naked eye limit of magnitude 6. Skywatchers with utterly dark conditions might glimpse stars as faint 7.5. My own personal best is 6.5.

With each drop in magnitude the number of stars you can see increases exponentially. There are only 22 first magnitude or brighter stars compared to 5,946 stars down to magnitude 6.

What appears blank at first is filled with stars -- 26 of them down to magnitude 6.3 are visible inside the Great Square from a dark sky site. How many can you see? Click for a large version. Source: Stellarium — What appears blank at first is filled with stars — 26 of them down to magnitude 6.3 are visible inside the Great Square from a dark sky site. How many can you see? Click for a larger version. Source: Stellarium

Ready to stretch your sight and rate your night sky? Step outside at nightfall and allow your eyes to dark-adapt for 20 minutes. With a copy of the map (above) in hand, start with the brightest stars and work your way to the faintest. Each every small step down the magnitude ladder prepares your eyes the next.

With a little effort you should be able to spot the four 4th magnitude range stars. At magnitude 5, you’ll work harder. Moving beyond 5.5 can be very challenging. I revert to averted vision to corral these fainties. Instead of staring directly at the star, play your eye around it. Look a bit to this side and that. This allows a rod-rich part of the retina that’s excellent at seeing faint stuff play through the scene and snatch up the faintest possible stars.

Magnitude scale showing the limits of the eye, binoculars and telescopes. Credit: Dr. Michael Bolte, UCO/Lick Observatory

From my house I can pick out about dozen points of light inside the Square on a moonless night. How many will you see? Once you know your magnitude limit, compare your result to John Bortle’s Dark Sky Scale … and weep. No, just kidding. But his Class 1 excellent sky includes a description of seeing stars down to magnitude 8 and the summer Milky Way casting shadows.

Hard to believe that before about 1790, when gas lighting was introduced in England, Class 1 skies were the norm across virtually the entire planet. Nowadays, most of us have to drive a hundred miles or more to experience true, untrammeled darkness.

Have fun with the challenge and let us know in the comments area how you do. Here’s hoping you find the Great Square far from vacant.

December 1, 2014December 23, 2015 by Elizabeth Howell

Probing Pluto’s Paltry Atmosphere Using A Solar Eclipse And Spacecraft

Artist's conception of the Pluto system from the surface of one of its moons. Credit: NASA, ESA and G. Bacon (STScI)

Pluto is so far away from us and so tiny that it’s hard to glean even basic facts about it. What is its tenuous atmosphere made of? And how to observe it during NASA’s New Horizons very brief flyby next July? A recent Johns Hopkins blog post explains how a careful maneuver post-Pluto will let investigators use the Sun to examine the dwarf planet’s true nature.

Investigators will use an instrument called Alice, an ultraviolet spectrometer, to look at the atmosphere around Pluto and its largest moon, Charon. Alice is capable of examining the gases in the atmosphere using a large “airglow” aperture (4 by 4 centimeters) and also using the Sun for observation with a smaller, 1-mm solar occultation channel.

“Once New Horizons flies past Pluto, the trajectory will conveniently (meaning, carefully planned for many years) fly the spacecraft through Pluto’s shadow, creating an effect just like a solar eclipse here on Earth,” wrote Joel Parker, New Horizons co-investigator, in a blog post.

“So we can (and will) just turn the spacecraft around and stare at the Sun, using Alice as it goes behind Pluto to measure how the Sun’s ultraviolet light changes as that light passes through deeper and deeper parts of Pluto’s atmosphere. This technique lets us measure the composition of Pluto’s atmosphere as a function of altitude.”

And guess where the technique was used not too long ago? Titan! That’s a moon of Saturn full of hydrocarbons and what could be a precursor chemistry to life. The moon is completely socked in with this orange haze that is intriguing. Scientists are still trying to figure out what it is made of — and also, to use our understanding of it to apply to planets outside our solar system.

When a huge exoplanet passes in front of its star, and it’s close enough to Earth, scientists are starting to learn how to ferret out information about its chemistry. This shows them what temperature the atmosphere is like and what it is made of, although it should be emphasized scientists are only starting on this work.

A composite image of Titan's atmosphere, created using blue, green and red spectral filters to create an enhanced-color view. Image Credit: NASA/JPL/Space Science Institute — A composite image of Titan’s atmosphere, created using blue, green and red spectral filters to create an enhanced-color view. Image Credit: NASA/JPL/Space Science Institute

The goal of performing these transit observations of Titan was to understand how haze on an exoplanet might blur the observations. From four passes with the Cassini spacecraft, the team (led by Tyler Robinson at NASA’s Ames Research Center) found that haze would make it difficult to get information from all but the upper atmosphere.

“An additional finding from the study is that Titan’s hazes more strongly affect shorter wavelengths, or bluer, colors of light,” NASA stated at the time. “Studies of exoplanet spectra have commonly assumed that hazes would affect all colors of light in similar ways. Studying sunsets through Titan’s hazes has revealed that this is not the case.”

The nature of Pluto will better come to light when New Horizons makes its pass by the planet in July 2015. Meanwhile, controllers are counting down the days until the spacecraft emerges from its last hibernation on Saturday (Dec. 6).

Source: Johns Hopkins Applied Physics Laboratory

November 19, 2014December 23, 2015 by David Dickinson

Observing Challenge: Watch Asteroid 3 Juno Occult a +7th Magnitude Star Tonight

One of the better asteroid occultations of 2014 is coming right up tonight, and Canadian and U.S. observers in the northeast have a front row seat.

The event occurs in the early morning hours of Thursday, November 20th, when the asteroid 3 Juno occults the 7.4 magnitude star SAO 117176. The occultation kicks off in the wee hours as the 310 kilometre wide “shadow” of 3 Juno touches down and crosses North America from 6:54 to 6:57 Universal Time (UT), which is 12:54 to 12:57 AM Central, or 1:54 to 1:57 AM Eastern Standard Time.

The path of tomorrow’s occultation along with the circumstances. Credit: Steve Preston’s Asteroid Occultation website.

The maximum predicted length of the occultation for observers based along the centerline is just over 27 seconds. Note that 3 Juno also shines at magnitude +8.5, so both it and the star are binocular objects. The event will sweep across Winnipeg and Lake of the Woods straddling the U.S. Canadian border, just missing Duluth Minnesota before crossing Lake Superior and over Ottawa and Montreal and passing into northern Vermont and New Hampshire. Finally, the path crosses over Portland Maine, and heads out to sea over the Atlantic Ocean.

Don’t live along the path? Observers worldwide will still see a close pass of 3 Juno and the +7^th magnitude star as both do their best to impersonate a close binary pair. If you’ve never crossed spotting 3 Juno off of your astro-“life list,” now is a good time to try.

The position of the target star HIP43357/SAO 117176 is:

Right Ascension: 8 Hours 49’ 54”

Declination: +2° 21’ 44”

A finder chart for 3 Juno and HIP43357. Stars are noted down to +10th magnitude. Created using Starry Night Education software.

Generally, the farther east you are along the track, the higher the pair will be above the horizon when the event occurs, and the better your observing prospects will be in terms of altitude or elevation. From Portland Maine — the last port of call for the shadow of 3 Juno on dry land — the pair will be 35 degrees above the horizon in the constellation of Hydra.

The projected sky cover at the time of the occultation. Credit: NWS/NOAA.

As always, the success in observing any astronomical event is at the whim of the weather, which can be fickle in North America in November. As of 48 hours out from the occultation, weather prospects look dicey, with 70%-90% cloud cover along the track. But remember, you don’t necessarily need a fully clear sky to make a successful observation… just a clear view near the head of Hydra asterism. Remember the much anticipated occultation of Regulus by the asteroid 163 Erigone earlier this year? Alas, it went unrecorded due to pesky but pervasive cloud cover. Perhaps this week’s occultation will fall prey to the same, but it’s always worth a try. In asteroid occultations as in free throws, you miss 100% of the shots that you don’t take!

IOTA — The path of the occcultation across eastern North America. Credit: Google Earth/BREIT IDEAS observatory.

Why study asteroid occultations? Sure, it’s cool to see a star wink out as an asteroid passes in front of it, but there’s real science to be done as well. Expect the star involved in Thursday’s occultation to dip down about two magnitudes (six times) in brightness. The International Occultation Timing Association (IOTA) is always seeking careful measurements of asteroid occultations of bright stars. If enough observations are made along the track, a shape profile of the target asteroid emerges. And the possible discovery of an “asteroid moon” is not unheard of using this method, as the background star winks out multiple times.

UT-Juno Occultation — 3 Juno as imaged by the 100″ Hooker telescope at the Mt. Wilson observatory at different wavelengths using adaptive optics. Credit: NASA/JPL/The Harvard Smithsonian Center for Astrophysics.

3 Juno was discovered crossing Cetus by astronomer Karl Harding on September 1^st, 1804 from the Lilienthal Observatory in Germany. The 3^rd asteroid discovered after 1 Ceres and 2 Pallas, 3 Juno ranks 5^th in size at an estimated 290 kilometres in diameter. In the early 19^th century, 3 Juno was also considered a planet along with these other early discoveries, until the ranks swelled to a point where the category of asteroid was introduced. A denizen of the asteroid belt, 3 Juno roams from 2 A.U.s from the Sun at perigee to 3.4 A.U.s at apogee, and can reach a maximum brightness of +7.4th magnitude as seen from the Earth. No space mission has ever been dispatched to study 3 Juno, although we will get a good look at its cousin 1 Ceres next April when NASA’s Dawn spacecraft enters orbit around the king of the asteroids.

3 Juno reaches opposition and its best observing position on January 29^th, 2015.

3 Juno also has an interesting place in the history of asteroid occultations. The first ever predicted and successfully observed occultation of a star by an asteroid involved 3 Juno on February 19^th, 1958. Another occultation involving the asteroid on December 11^th, 1979 was even more widely observed. Only a handful of such events were caught prior to the 1990s, as it required ultra-precise computation and knowledge of positions and orbits. Today, dozens of asteroid occultations are predicted each month worldwide.

Observing an asteroid occultation can be challenging but rewarding. You can watch Thursday’s event with binoculars, but you’ll want to use a telescope to make a careful analysis. You can either run video during the event, or simply watch and call out when the star dims and brightens as you record audio. Precise timing and pinpointing your observing location via GPS is key, and human reaction time plays a factor as well. Be sure to locate the target star well beforehand. For precise time, you can run WWV radio in the background.

And finally, you also might see… nothing. Asteroid paths have a small amount of uncertainty to them, and although these negative observations aren’t as thrilling to watch, they’re important to the overall scientific effort.

Good luck, and let us know of your observational tales of anguish and achievement!

October 17, 2014December 23, 2015 by Elizabeth Howell

Solar ‘Bombs’ And Mini-Tornadoes Spotted By Sun-Watching Spacecraft

An image of a May 9, 2014 coronal mass ejection from the Sun using data from both the Interface Region Imaging Spectrograph (IRIS) spacecraft and the Solar Dynamics Observatory. Credit: NASA, Lockheed Martin Solar & Astrophysics Laboratory

My, the Sun is a violent place. I mean, we knew that already, but there’s even more evidence for that using new data from a brand-new NASA spacecraft. There’s talk now about tornadoes and jets and even “bombs” swirling amid our Sun’s gassy environment.

A huge set of results from NASA’s Interface Region Imaging Spectrograph (IRIS) spacecraft reveals the true nature of a mysterious transition zone between Sun’s surface and the corona, or atmosphere. Besides the pretty fireworks and videos, these phenomena are telling scientists more about how the Sun moves energy from the center to the outskirts. And, it could tell us more about how stars work in general.

The results are published in five papers yesterday (Oct. 15) in Science magazine. Below, a brief glimpse of what each of these papers revealed about our closest star.

Bombs

This is a heck of a lot of energy packed in here. Raging at temperatures of 200,000 degrees Fahrenheit (111,093 degrees Celsius) are heat “pockets” — also called “bombs” because they release energy quickly. They were found lower in the atmosphere than expected. The paper is here (led by Hardi Peter of the Max Planck Institute for Solar System Research in Gottingen, Germany.)

Tornadoes

It’s a twist! You can see some structures in the chromosphere, just above the Sun’s surface, showing gas spinning like a tornado. They spin around as fast as 12 miles (19 kilometers) a second, which is considered slow-moving on the Sun. The paper is here (led by Bart De Pontieu, the IRIS science lead at Lockheed Martin in California).

High-speed jets

Artist's impression of the solar wind from the sun (left) interacting with Earth's magnetosphere (right). Credit: NASA — Artist’s impression of the solar wind from the sun (left) interacting with Earth’s magnetosphere (right). Credit: NASA

How does the solar wind — that constant stream of charged particles that sometimes cause aurora on Earth — come to be? IRIS spotted high-speed jets of material moving faster than ever observed, 90 miles (145 kilometers) a second. Since these jets are emerging in spots where the magnetic field is weaker (called coronal holes), scientists suspect this could be a source of the solar wind since the particles are thought to originate from there. The paper is here (led by Hui Tian at the Harvard-Smithsonian Center for Astrophysics in Massachusetts.)

Nanoflares

A solar filament erupts with a coronal mass ejection in this image captured by NASA's Solar Dynamics Observatory in August 2012. Credit: NASA's GSFC, SDO AIA Team — A solar filament erupts with a coronal mass ejection in this image captured by NASA’s Solar Dynamics Observatory in August 2012. Credit: NASA’s GSFC, SDO AIA Team

Those solar flares the Sun throws off happen when magnetic field lines cross and then snap back into place, flinging particles into space. Nanoflares could do the same thing to heat up the corona, and that’s something else that IRIS is examining. The paper is here (led by Paola Testa, at the Harvard-Smithsonian Center for Astrophysics.)

Structures and more

And here is the transition region in glorious high-definition. Improving on data from the Skylab space station in the 1970s (bottom of video), you can see all sorts of mini-structures on the Sun. The more we learn about these 2,000-mile (3,220-km) objects, the better we’ll understand how heating moves through the Sun. The paper is here (led by Viggo Hansteen, at the University of Oslo in Norway.)

Source: NASA

October 15, 2014December 23, 2015 by Tim Reyes

Old Equations Shed New Light on Quasars

An artists illustration of the early Universe. Image Credit: NASA

There’s nothing more out of this world than quasi-stellar objects or more simply – quasars. These are the most powerful and among the most distant objects in the Universe. At their center is a black hole with the mass of a million or more Suns. And these powerhouses are fairly compact – about the size of our Solar System. Understanding how they came to be and how — or if — they evolve into the galaxies that surround us today are some of the big questions driving astronomers.

Now, a new paper by Yue Shen and Luis C. Ho – “The diversity of quasars unified by accretion and orientation” in the journal Nature confirms the importance of a mathematical derivation by the famous astrophysicist Sir Arthur Eddington during the first half of the 20th Century, in understanding not just stars but the properties of quasars, too. Ironically, Eddington did not believe black holes existed, but now his derivation, the Eddington Luminosity, can be used more reliably to determine important properties of quasars across vast stretches of space and time.

A quasar is recognized as an accreting (meaning- matter falling upon) super massive black hole at the center of an “active galaxy”. Most known quasars exist at distances that place them very early in the Universe; the most distant is at 13.9 billion light years, a mere 770 million years after the Big Bang. Somehow, quasars and the nascent galaxies surrounding them evolved into the galaxies present in the Universe today. At their extreme distances, they are point-like, indistinguishable from a star except that the spectra of their light differ greatly from a star’s. Some would be as bright as our Sun if they were placed 33 light years away meaning that they are over a trillion times more luminous than our star.

An artists illustration of the central engine of a Quasar. These "Quasi-stellar Objects" QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA) — An artists illustration of the central engine of a quasar. These “Quasi-stellar Objects” QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)

The Eddington luminosity defines the maximum luminosity that a star can exhibit that is in equilibrium; specifically, hydrostatic equilibrium. Extremely massive stars and black holes can exceed this limit but stars, to remain stable for long periods, are in hydrostatic equilibrium between their inward forces – gravity – and the outward electromagnetic forces. Such is the case of our star, the Sun, otherwise it would collapse or expand which in either case, would not have provided the stable source of light that has nourished life on Earth for billions of years.

Generally, scientific models often start simple, such as Bohr’s model of the hydrogen atom, and later observations can reveal intricacies that require more complex theory to explain, such as Quantum Mechanics for the atom. The Eddington luminosity and ratio could be compared to knowing the thermal efficiency and compression ratio of an internal combustion engine; by knowing such values, other properties follow.

Several other factors regarding the Eddington Luminosity are now known which are necessary to define the “modified Eddington luminosity” used today.

The new paper in Nature shows how the Eddington Luminosity helps understand the driving force behind the main sequence of quasars, and Shen and Ho call their work the missing definitive proof that quantifies the correlation of a quasar properties to a quasar’s Eddington ratio.

They used archival observational data to uncover the relationship between the strength of the optical Iron [Fe] and Oxygen[O III] emissions – strongly tied to the physical properties of the quasar’s central engine – a super-massive black hole, and the Eddington ratio. Their work provides the confidence and the correlations needed to move forward in our understanding of quasars and their relationship to the evolution of galaxies in the early Universe and up to our present epoch.

Astronomers have been studying quasars for a little over 50 years. Beginning in 1960, quasar discoveries began to accumulate but only through radio telescope observations. Then, a very accurate radio telescope measurement of Quasar 3C 273 was completed using a Lunar occultation. With this in hand, Dr. Maarten Schmidt of California Institute of Technology was able to identify the object in visible light using the 200 inch Palomar Telescope. Reviewing the strange spectral lines in its light, Schmidt reached the right conclusion that quasar spectra exhibit an extreme redshift and it was due to cosmological effects. The cosmological redshift of quasars meant that they are at a great distance from us in space and time. It also spelled the demise of the Steady-State theory of the Universe and gave further support to an expanding Universe that emanated from a singularity – the Big Bang.

Dr. Maarten Schmidt, Caltech University, with Donald Lynden-Bell, were the first recipients of the Kavli Prize in Astrophysics, “for their seminal contributions to understanding the nature of quasars”. While in high school, this author had the privilege to meet Dr. Schmidt at the Los Angeles Museum of Natural History after his presentation to a group of students. (Photo Credit: Caltech) — Dr. Maarten Schmidt, Caltech, with Donald Lynden-Bell, were the first recipients of the Kavli Prize in Astrophysics, “for their seminal contributions to understanding the nature of quasars”. While in high school, this author had the privilege to meet Dr. Schmidt at the Los Angeles Museum of Natural History after his presentation to a group of students. (Photo Credit: Caltech)

The researchers, Yue Shen and Luis C. Ho are from the Institute for Astronomy and Astrophysics at Peking University working with the Carnegie Observatories, Pasadena, California.

References and further reading:

“The diversity of quasars unified by accretion and orientation”, Yue Shen, Luis C. Ho, Sept 11, 2014, Nature

“What is a Quasar?”, Universe Today, Fraser Cain, August 12, 2013

“Interview with Maarten Schmidt”, Caltech Oral Histories, 1999

“Fifty Years of Quasars, a Symposium in honor of Maarten Schmidt”, Caltech, Sept 9, 2013

October 10, 2014December 29, 2015 by Tim Reyes

Nearby Galaxy Holds First Ultraluminous X-Ray Source that is a Pulsar

Artist's illustration of a rotating neutron star, the remnants of a super nova explosion. Credit: NASA, Caltech-JPL

A research team led by Caltech astronomers of Pasadena California have discovered an ultraluminous X-ray (ULX) source that is pulsating. Their analysis concluded that the source in a nearby galaxy – M82 – is from a rotating neutron star, a pulsar. This is the first ULX source attributed to a pulsar.

Matteo Bachetti of the Université de Toulouse in France first identified the pulsating source and is the lead author of the paper, “An ultraluminous X-ray source powered by an accreting neutron star” in the journal Nature. Caltech astronomer Dr. Fiona Harrison, the team leader, stated “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.”

What is most extraordinary is that this discovery places even more strain on theories already hard pressed to explain the existence of ultraluminous X-Ray sources. The burden falls on the shoulder of the theorists.

The source of the observations is the NuSTAR space telescope, a SMEX class NASA mission. It is a Wolter telescope that uses grazing incidence optics, not glass (refraction) or mirrors (reflection) as in visible light telescopes. The incidence angle of the X-rays must be very shallow and consequently the optics are extended out on a 10 meter (33 feet) truss. NuSTAR records its observations with a time stamp such as taking a video of the sky. The video recording in high speed is not in visible everyday light but what is called hard x-rays. Only gamma rays are more energetic. X-rays emanate from the most powerful sources and events in the Universe. NuStar observes in the energy range of X-Rays from 5 to 80 KeV (electron volt)while the famous Chandra space telescope observes in the .1 to 10 KeV range. Chandra is one NASA’s great space telescope, was launched by the Space Shuttle Columbia (STS-93) in 1999. Chandra has altered our view of the Universe as dramatically as the first telescope constructed by Galileo. NuSTAR carries on the study of X-rays to higher energies and with greater acuity.

ULX sources are rare in the Universe but this is the first pulsating ULX. After analysis, they concluded that this is not a black hole but rather its little brother, a spinning neutron star as the source. More specifically, this is an accreting binary pulsar; matter from a companion star is being gravitationally attracted by and accreting onto the pulsar.

The Crab Nebula Pulsar, M1. Both are sequences of observations that show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech) — The prime example of a pulsar – the Crab Nebula Pulsar, M1. These actual observations show the expansion of shock waves emanating from the Pulsar interacting with the surrounding nebula. The Crab Pulsar actually pulsates 30 times per second, not seen here, a result of its rotation rate and the relative offset of the magnetic pole. Charndra X-Rays (left), Hubble Visible light (right). (Credit: NASA, JPL-Caltech)

Take a neutron star and spin it up to anywhere from 700 rotations per second to a mere one rotation every 10 seconds. Now you have a neutron star called a pulsar. Spinning or not, these are the remnants of supernovae, stellar explosions that can outshine a galaxy of 300 billion stars. Just one teaspoon of neutron star material weighs 10 million tons (9,071,847,400 kg). That is the same weight as 900 Great Pyramids of Giza all condensed to one teaspoon. As incredible a material and star that a neutron star is, they were not thought to be the source of any ultraluminous X-Ray sources. This view has changed with the analysis of observations by this research team utilizing NuSTAR. The telescope name – NuSTAR – stands for Nuclear Spectroscopic Telescope Array.

There is nothing run of the mill about black holes. Dr. Stephen Hawking only conceded after 25 years, in 2004 (the Thorne-Hawking Bet) that Black Holes exist. And still today it is not absolutely certain. Recall the Universe Today weekly – Space Hangout on September 26 – “Do Black Holes exist?” and the article by Jason Major, “There are no such things as Black Holes.”

Pulsars stars are nearly as exotic as black holes, and all astronomers accept the existence of these spinning neutron stars. There are three final states of a dying star. Stars like our Sun at the end of their life become very dense White Dwarf stars, about the size of the Earth. Neutron stars are the next “degenerate” state of a dying exhausted star. All the electrons have merged with the protons in the material of the star to become neutrons. A neutron star is a degenerate form of matter effectively made up of all neutron particles. Very dense, these stars are really small, the size of cities, about 16 miles in diameter. The third type of star in its final state is the Black Hole.

The Crab Nebula was first observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova, Chinese astronomers observed in 1054 A.D and holds the second Pular discovered (1968). — The Crab Nebula was first observed in the 1700s and is catalogued Messier object, M1. The remant explosion of a SuperNova that Chinese astronomers observed in 1054 A.D, it holds the second Pulsar discovered (1968).

A spinning neutron star creates a magnetic field, the most powerful of such fields in the Universe. They are like a dipole of a bar magnet and because of how magnetic fields confine the hot gases – plasma – of the neutron star, constant streams of material flow down and light streams out from the magnetic poles.

Recently, the Earth has had incredible northern lights, aurora. These lights are also from hot gases — a plasma — at the top of our atmosphere. Likewise, hot energetic particles from the Sun are funneled down into the magnetic poles of the Earth’s field that creates the northern lights. For spinning neutron stars – pulsars – the extreme light from the magnetic poles are like beacons. Just like our Earth, the magnetic poles and the spin axis poles do not coincide. So the intense beacon of light will rotate around and periodically point at the Earth. The video of the first illustration describes this action.

Messier object - M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar. — Messier object – M82, the Cigar Nebula, nicknamed for the shape seen through telescopes of the 1800s. This is the location of the newly discovered Pulsar.

The light beacons from pulsars are very bright but theory, until now, has been supported by observations. No ultraluminous X-ray sources should be pulsars. The newly discovered pulsar is outputting 100 times more energy than any other. Discoveries like the one by these astronomers utilizing NuSTAR is proof that there remains more to discover and understand and new telescopes will be conceived to help resolve questions raised by NuSTAR or Chandra.

How to Turn Your Phone Into A Cosmic Ray Detector

Artist's impression of cosmic rays striking Earth (Simon Swordy/University of Chicago, NASA)

Quick, do you have an Android phone in your pocket? A few small changes and you could help physicists probe more of the curious nature of cosmic rays, high-energy particles that emanate from outside our solar system.

Just download an app, cover up your phone’s camera with duct tape, then place it somewhere (running idle) with the screen facing up. If a particle “event” happens, the information will be logged in a central database.

The project (called Distributed Electronic Cosmic-ray Observatory or DECO) aims to record secondary particles called muons that occur when cosmic rays hit the Earth’s atmosphere. Scientists believe cosmic rays are created in black holes and supernovas, but more studies are needed.

Screenshot of an Android app developed at the University of Wisconsin-Madison that aims to capture cosmic rays. Credit: Justin Vandenbroucke

Researchers at the Wisconsin IceCube Particle Astrophysics Center (WIPAC), led by Justin Vandenbroucke, note that there are things about cosmic rays that confuse physicists. Their paths in space change as they go across magnetic fields, and it makes searching for other astronomy events difficult. That’s where they hope the phone study will be useful.

“Smartphone cameras use silicon chips that work through what is called the photoelectric effect, in which particles of light, or photons, hit a silicon surface and release an electric charge,” the University of Wisconsin-Madison wrote in a press release.

“The same is true for muons. When a muon strikes the semiconductor that underpins a smartphone camera, it liberates an electric charge and creates a signature in pixels that can be logged, stored and analyzed.”

For more details on how to run and use the app, consult this page (it’s the second item).

Source: University of Wisconsin-Madison