Posted on by Jon Voisey

Type II-P Supernovae as a New Standard Candle

Artist illustration of a supernova. Image credit: ESO

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Much of astronomical knowledge is built on the cosmic distance ladder. This ladder is built to determine distances to objects in our sky. Low lying rungs for nearby objects are used to calibrate the methodology for more distant objects which are, in turn, used to calibrate for more distant objects and so on. One of the reason so many runs need to be added is that techniques often become difficult to impossible to used past a certain distance. Cepheid Variables are a fantastic object to allow us to measure distances, but their luminosity is only sufficient to allow us to detect them to a few tens of millions of parsecs. As such, new techniques, based on brighter objects must be developed.

The most famous of these is the use of Type Ia Supernovae (ones that collapse just pass the Chandrasekhar limit) as “standard candles”. This class of objects has a well defined standard luminosity and by comparing its apparent brightness to the actual brightness, astronomers can determine distance via the distance modulus. But this relies on the fortuitous circumstance of having such an event occur when you want to know the distance! Obviously, astronomers need some other tricks up their sleeve for cosmological distances, and a new study discusses the possibility of using another type of supernova (SN II-P) as another form of standard candles.

Type II-P supernovae are classical, core-collapse supernovae that occur when the core of a star has passed the critical limit and can no longer support the mass of the star. But unlike other supernovae, the II-P decays more slowly, leveling off for some time creating a “plateau” in the light curve (which is where the “P” comes from). Although their plateaus are not all at the same brightness, making them initially useless as a standard candle, studies over the past decade have shown that observing other properties may allow astronomers to determine what the brightness of the plateau actually is and making these supernovae “standardizable”.

In particular, discussion has been centering recently around possible connections between the velocity of ejecta and the brightness of the plateau. A study published by D’Andrea et al. earlier this year attempted to link the absolute brightness to the velocities of the Fe II line at 5169 Angstroms. However, this method left large experimental uncertainties which translated to an error of up to 15% of the distance.

A new paper, to be published in October’s issue of the Astrophysical Journal, a new team, led by Dovi Poznanski of the Lawrence Berkley National Laboratory attempts to reduce these errors by utilizing the hydrogen beta line. One of the primary advantages to this is that hydrogen is much more plentiful allowing the hydrogen beta line to stand out whereas the Fe II lines tend to be weak. This improves the signal to noise (S/N) ratio and improves overall data.

Using data from the Sloan Digital Sky Survey (SDSS), the team was able to decrease the error in distance determination to 11%. Although this was an improvement over the D’Andrea et al. study, it is still significantly higher than many other methods for distance determination at similar distances. Poznanski suggests that this data is likely skewed due to a natural bias towards brighter supernovae. This systematic error stems from the fact that the SDSS data is supplemented up with follow-up data which the team employed, but the follow-ups are only conducted if the supernova meets certain brightness criteria. As such, their method is not fully representative of all supernovae of this type.

To improve their calibration and hopefully improve the method, the team plans to continue their study with expanded data from other studies that would be free of such biases. In particular the team intends to use the Palomar Transient Factory to supplement their results.

As the statistics improve, astronomers will gain another rung on the cosmological distance ladder, but only if they’re lucky enough to find one of this type of supernova.

Posted on by Jerry Coffey

What Is An Electron

Faraday's Constant

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What is an electron? Easily put, an electron is a subatomic particle that carries a negative electric charge. There are no known components, so it is believed to be an elementary particle(basic building block of the universe). The mass of an electron is 1/1836 of its proton. Electrons have an antiparticle called a positron. Positrons are identical to electrons except that all of its properties are the exact opposite. When electrons and positrons collide, they can be destroyed and will produce a pair (or more) of gamma ray photons. Electrons have gravitational, electromagnetic, and weak interactions.

In 1913, Niels Bohr postulated that electrons resided in quantized energy states, with the energy determined by the spin(angular momentum)of the electron’s orbits and that the electrons could move between these orbits by the emission or absorption of photons. These orbits explained the spectral lines of the hydrogen atom. The Bohr model failed to account for the relative intensities of the spectral lines and it was unsuccessful in explaining the spectra of more complex atom. Gilbert Lewis proposed in 1916 that a ‘covalent bond’ between two atoms is maintained by a pair of shared electrons. In 1919, Irving Langmuir improved on Lewis’ static model and suggested that all electrons were distributed in successive “concentric(nearly) spherical shells, all of equal thickness”. The shells were divided into a number of cells containing one pair of electrons. This model was able to qualitatively explain the chemical properties of all elements in the periodic table.

The invariant mass of an electron is 9.109×10-31 or 5.489×10-4 of the atomic mass unit. According to Einstein’s principle of mass-energy equivalence, this mass corresponds to a rest energy of .511MeV. Electrons have an electric charge of -1.602×10 coulomb. This a standard unit of charge for subatomic particles. The electron charge is identical to the charge of a proton. In addition to spin, the electron has an intrinsic magnetic moment along its spin axis. It is approximately equal to one Bohr magneton. The orientation of the spin with respect to the momentum of the electron defines the property of elementary particles known as helicity. Observing a single electron shows the upper limit of the particle’s radius is 10-22 meters. Some elementary particles decay into less massive particles. But an electron is thought to be stable on the grounds that it is the least massive particle with non-zero electric charge.

Understanding what is an electron is to begin to understand the basic building blocks of the universe. A very elementary understanding, but a building block to great scientific thought.

We have written many articles about the electron for Universe Today. Here’s an article about the Electron Cloud Model, and here’s an article about the charge of electron.

If you’d like more info on the Electron, check out the History of the Electron Page, and here’s a link to the article about Killer Electrons.

We’ve also recorded an entire episode of Astronomy Cast all about the Composition of the Atom. Listen here, Episode 164: Inside the Atom.

Posted on by Jon Voisey

The Thick Disk: Galactic Construction Project or Galactic Rejects?

Our Milky Way Gets a Makeover
Our Milky Way Gets a Makeover

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The disk of spiral galaxies is comprised of two main components: The thin disk holds the majority of stars and gas and is the majority of what we see and picture when we think of spiral galaxies. However, hovering around that, is a thicker disk of stars that is much less populated. This thick disk is distinct from the thin disk in several regards: The stars there tend to be older, metal deficient, and orbit the center of the galaxy more slowly.

But where this population of the stars came from has been a long standing mystery since its identification in the mid 1970’s. One hypothesis is that it is the remainder of cannibalized dwarf galaxies that have never settled into a more standard orbit. Others suggest that these stars have been flung from the thin disk through gravitational slingshots or supernovae. A recent paper puts these hypothesis to the observational test.

At a first glance, both propositions seem to have a firm observational footing. The Milky Way galaxy is known to be in the process of merging with several smaller galaxies. As our galaxy pulls them in, the tidal effects shred these minor galaxies, scattering the stars. Numerous tidal streams of this sort have been discovered already. The ejection from the thin disk gains support from the many known “runaway” and “hypervelocity” stars which have sufficient velocity to escape the thin disk, and in some cases, the galaxy itself.

The new study, led by Marion Dierickx of Harvard, follows up on a 2009 study by Sales et al., which used simulations to examine the features stars would take in the thick disk should they be created via these methods. Through these simulations, Sales showed that the distribution of eccentricities of the orbits should be different and allow a method by which to discriminate between formation scenarios.

By using data from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), Dierickx’s team compared the distribution of the stars in our own galaxy to the predictions made by the various models. Ultimately, their survey included some 34,000 stars. By comparing the histogram of eccentricities to that of Sales’ predictions, the team hoped to find a suitable match that would reveal the primary mode of creation.

The comparison revealed that, should ejection from the thin disk be the norm there were too many stars in nearly circular orbits as well as highly eccentric ones. In general, the distribution was too wide. However, the match for the scenario of mergers fit well lending strong credence to this hypothesis.

While the ejection hypothesis or others can’t be ruled out completely, it suggests that, at least in our own galaxy, they play a rather minor role. In the future, additional tests will likely be employed, analyzing other aspects of this population.

Posted on by Jason Rhian

Space Shuttle Discovery’s Last Rollover to the VAB

Discovery pauses on her way to the Vehicle Assembly Building (VAB). This marks the last time that this shuttle will make this trip. Photo Credit: Jason Rhian

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Rollover, the name itself is not all that awe-inspiring, the sight however; will take one’s breath away. The Discovery space shuttle emerged from its technological cocoon located in Orbiter Processing Facility-3 (OPF-3) at 7 a.m. EDT on Sept. 9, 2010 and was moved into the expansive Vehicle Assembly Building (VAB) a few hours later. The short, but slow trek allowed workers, many of whom have spent their entire careers servicing the orbiter, to pose with Discovery as she made this voyage. 

Discovery’s trip to the VAB was delayed a day from Wednesday to Thursday, due to a broken water main. Workers found the break in a pipe located near the VAB and repaired it enough to allow second-shift workers to go to work later in the day. 

“The pipe that broke was 50 years old,” said Allard Beutel, a NASA Public Affairs Officer. “The Kennedy team managed to have a work-around in place in under a day.” 

Rollover is an important milestone on the road to flight. In this case, the occasion was all the more historic as it marked Discovery’s final trip to the VAB for this reason. The orbiter is flanked by workers that have worked to see that the shuttle is prepared for flight. They act as guides ensuring that there is no debris along the short drive that the transport vehicle takes from OPF-3 to the VAB. There were several stops along the way to allow photographs to be taken; marking the last time that Discovery is scheduled to move to the VAB in preparation for flight. 

Once inside the VAB Discovery was connected to a crane that hoisted the 171,000 lb. space glider into the air. From there it is mated to a set of Solid Rocket Boosters (SRB) and External Tank (ET) waiting for the orbiter’s arrival. Seeing this massive spacecraft hanging in mid-air alters one’s perceptions about the U.S. space program. It places a powerful spotlight onto the efforts required to put astronauts into orbit. 

Windswept clouds encircle Discovery as the shuttle is moved to the Vehicle Assembly Building. Photo Credit: Jason Rhian

Approximately two weeks after the shuttle is mated the “full stack” is then ready to head to Launch Complex 39A. This marks the next phase in the path to launch – Rollout. 

Discovery will deliver and install the Leonardo Permanent Multipurpose Module (PMM), the Express Logistics Carrier 4 and provide much-needed spare parts to the International Space Station (ISS). This will be the 35th shuttle mission to the space station. The crew of STS-133 consists of Commander Steven Lindsey, Pilot Eric Boe and Mission Specialists Alvin Drew, Michael Barratt, Tim Kopra and Nicole Stott. 

Although STS-133 will mark the final time that Discovery is slated to take to the skies there had been talk that she could potentially ride to orbit on STS-135. However, if that mission is approved it is likely Atlantis will be the orbiter selected for that flight. Currently, STS-133 onboard Discovery is scheduled to launch from Kennedy Space Center on Nov. 1, 2010 at 4:40 p.m. EDT.

Posted on by Jon Voisey

Follow-up Studies on June 3rd Jupiter Impact

Color image of impact on Jupiter on June 3, 2010. Credit: Anthony Wesley

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Poor Jupiter just can’t seem to catch a break. Ever since 1994, when our largest planet was hit by Comet Shoemaker-Levy, detections of impacts on Jupiter have occurred with increasing regularity. Most recently, an impact was witnessed on August 20. On June 3rd of 2010, (coincidentally the same day pictures from Hubble were released from a 2009 impact) Jupiter was hit yet again. Shortly after the June 3rd impact, several other telescopes joined the observing.

A paper to appear in the October issue of The Astrophysical Journal Letters discusses the science that has been gained from these observations.

The June 3rd impact was novel in several respects. It was the first unexpected impact that was reported from two independent locations simultaneously. Both discoverers were observing Jupiter with aims of engaging in a bit of astrophotography. Their cameras were both set to take a series of quick images, each lasting a fifth to a tenth of a second. This short time duration is the first time astronomers have had the ability to recreate the light curve for the meteor. Additionally, both observers were using different filters (one red and one blue) allowing for exploration of the color distribution.

Analysis of the light curve revealed that the flash lasted nearly two seconds and was not symmetric; The decay in brightness occurred faster than the increase at onset. Additionally, the curve showed several distinct “bumps” which indicated a flickering that is commonly seen on meteors on Earth.

The light released in the burning up of the object was used to estimate the total energy-released and in turn the mass of the object.  The total energy released was estimated to be between roughly (1.0–4.0) × 1015 Joules (or 250–1000 kilotons).

Follow-up observations from Hubble three days later revealed no scars from the impact. In the July 2009 impact, a hole punched in the clouds remained for several days. This indicated the object in the June 3 impact was considerably smaller and burned up before it was able to reach the visible cloud decks.

Observations intended to find debris came up empty. Infrared observations showed that no thermal signature was left even as little as 18 hours following the discovery.

Assuming that the object was an asteroid with a relative speed of ~60 km/sec and a density of ~2 g/cm3, the team estimated the size of the object to be between 8 and 13 meters, similar to the size of the two asteroids that recently passed Earth. This represents the smallest meteor yet observed on Jupiter. An object of similar size was estimated to be responsible for the impact on Earth in 1994 near the Marshall Islands. Estimates “predict objects of this size to collide with our planet every 6–15 years” with significantly higher rates on Jupiter ranging from one to one hundred such events annually.

Clearly, amateur observations led to some fantastic science. Modest telescopes, “in the range 15–20 cm in diameter equipped with webcams and video recorders” can easily allow for excellent coverage of Jupiter and continued observation could help in determining the impact rate and lead to a better understanding of the population of such small bodies in the outer solar system.

Posted on by Jon Voisey

Do Stars Really Form in Clusters?

The long standing view on the formation of stars is that they form in clusters. This theory is supported by understanding of the formation process that requires large clouds of gas and dust to be able to condense. Small clouds with enough mass to only form one star just can’t meet the required conditions to condense. In a large cloud, where conditions are sufficient, once one star begins, the feedback effects from this star will trigger other star formation. Thus, if you get one, you’ll likely get lots.

But a new paper takes a critical look at whether or not all stars really form in clusters.

The main difficulty in answering this question boils down to a simple question: What does it mean to be “in” a cluster. Generally, members of a cluster are stars that are gravitationally bound. But as time passes, most clusters shed members as gravitational interactions, both internal and external, remove outer members. This blurs the boundary between being bound and unbound.

Similarly, some objects that can initially look very similar to clusters can actually be groups known as an association. As the name suggests, while these stars are in close proximity, they are not truly bond together. Instead, their relative velocities will cause the the group to disperse without the need for other effects.

As a result, astronomers have considered other requirements to truly be a member of a cluster. In particular for forming stars, there is an expectation that cluster stars should be able to interact with one-another during the formation process.

Its these considerations that this new team uses as a basis, led by Eli Bressert from the University of Exeter. Using observations from Spitzer, the team analyzed 12 nearby star forming regions. By conducting the survey with Spitzer, an infrared telescope, the team was able to pierce the dusty veil that typically hides such young stars.

By looking at the density of the young stellar objects (YSOs) in the plane of the sky, the team attempted to determine just what portion of stars could be considered true cluster members under various definitions. As might be expected, the answer was highly dependent on the definition used. If a loose and inclusive definition was taken, they determined that 90% of YSOs would be considered as part of the forming cluster. However, if the definition was drawn at the narrow end, the percentage dropped as low as 40%. Furthermore, if the additional criterion of needing to be in such proximity that their “formation/evolution (along with their circumstellar disks and/or planets) may be affected by the close proximity of their low-mass neighbours”, the percentage dropped to a scant 26%.

As with other definition boundaries, the quibbling may seem little more than a distraction. However, with such largely varying numbers attached to them, these triflings carry great significance since inconsistent definitions can greatly distort the understanding. This study highlights the need for clarity in definitions for which astronomers constantly struggle in a muddled universe full overlapping populations and shades of gray.

Posted on by Nicholos Wethington

NASA to Send a Probe Into the Sun

An artist's impression of the Solar Probe Plus satellite, which will fly into the corona of the Sun to get an unprecedented look at how our Sun works. Image Credit: NASA

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NASA recently announced its choices for the experiments to fly aboard the Solar Probe Plus spacecraft, which is slated to launch no later than 2018. This spacecraft will perform the unprecedented task of flying into the Sun’s atmosphere – or corona – to take measurements of the plasma, magnetic fields and dust that surround our nearest star. It will be the first human-made satellite to approach the Sun at such a close proximity.

The previous record-holder for a spacecraft that approached the Sun was Helios 2, which came within 27 million miles (43.5 million kilometers) of the Sun in 1976. Solar Probe Plus will shatter that record, flying to 3.7 million miles (5.9 million kilometers) of the Sun’s surface at its closest approach. In flying so close to the Sun, the spacecraft will be able to get amazingly detailed data on the structure of the atmosphere that surrounds the Sun.

As you can imagine, it gets a little toasty as one gets that close to the Sun. Solar Probe Plus will utilize a special heat shield made of an 8-foot (2.4 m), 4.5 inch (11 cm)-thick special carbon-composite foam plate that will protect the craft from temperatures of up to 2600 degrees Fahrenheit (1400 degrees Celsius) and intense solar radiation. The heat shield is a modified version of that which was used in the MESSENGER mission to Mercury.

NASA has chosen five science projects out of the thirteen that were proposed since 2009. The selected proposals are, according to the press release:

— Solar Wind Electrons Alphas and Protons Investigation: principal investigator, Justin C. Kasper, Smithsonian Astrophysical Observatory in Cambridge, Mass. This investigation will specifically count the most abundant particles in the solar wind — electrons, protons and helium ions — and measure their properties. The investigation also is designed to catch some of the particles in a special cup for direct analysis.
— Wide-field Imager: principal investigator, Russell Howard, Naval Research Laboratory in Washington. This telescope will make 3-D images of the sun’s corona, or atmosphere. The experiment actually will see the solar wind and provide 3-D images of clouds and shocks as they approach and pass the spacecraft. This investigation complements instruments on the spacecraft providing direct measurements by imaging the plasma the other instruments sample.
— Fields Experiment: principal investigator, Stuart Bale, University of California Space Sciences Laboratory in Berkeley, Calif. This investigation will make direct measurements of electric and magnetic fields, radio emissions, and shock waves that course through the sun’s atmospheric plasma. The experiment also serves as a giant dust detector, registering voltage signatures when specks of space dust hit the spacecraft’s antenna.
— Integrated Science Investigation of the Sun:principal investigator, David McComas of the Southwest Research Institute in San Antonio. This investigation consists of two instruments that will take an inventory of elements in the sun’s atmosphere using a mass spectrometer to weigh and sort ions in the vicinity of the spacecraft.
— Heliospheric Origins with Solar Probe Plus: principal investigator, Marco Velli of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Velli is the mission’s observatory scientist, responsible for serving as a senior scientist on the science working group. He will provide an independent assessment of scientific performance and act as a community advocate for the mission.

Two important questions that the mission hopes to answer is the perplexing mystery of why the Sun’s atmosphere is hotter than its surface, and the mechanism for the solar wind that emanates from the Sun into the Solar System. The spacecraft will have a front-row seat to watch the solar wind speed up from subsonic to supersonic speed.

Because of the conservation of momentum, it takes a lot of slowing down to send a spacecraft towards the Sun. The Earth and objects on the Earth are traveling around the Sun at an average of 30 kilometers per second (67,000 miles per hour). So, to slow the spacecraft down enough to get it close to the Sun, it will have to fly around Venus seven times! This is the opposite of a gravity assist, or “slingshot”, in which a satellite gains energy by flying by a planet. In the case of Solar Probe Plus, as well as that of MESSENGER, multiple flybys of Venus imparts some of the craft’s energy to Venus, thereby slowing down the spacecraft.

The Solar Probe Plus mission is part of NASA’s “Living With a Star Program”, of which the Solar Dynamics Observatory is also a mission. This program is designed to study the impact our Sun has on the space environment of the Solar System, and acquire data to better equip future space missions.

Source: NASA press release, APL mission site

Posted on by Tega Jessa

What Are Clouds Made Of?

Clouds

When we think of clouds we think of those white cotton ball masses in the air. What we don’t really think about is what are clouds made of. We all know about the water cycle in some form. We know that clouds are created from the water that evaporates from various lakes, rivers, and oceans. We also know that at some time this evaporated water becomes rain and starts the cycle all over again.

However there are important questions about clouds we overlook. First, how are clouds visible if water vapor is normally supposed to be invisible like air or at least dissipate quickly after the first gush of steam? Second, why do clouds last so long in their different forms? Finally, what gives clouds their white or grey colors? As you can see there is a lot we take for granted in our understanding of clouds and how they are formed.

We know that clouds are made of water vapor, what we don’t know or at least forget is the important role that condensation plays in making clouds visible. For the most part water vapor is invisible. This is proven by the fact that the air we breathe regularly has some water vapor as part of its composition. However we don’t see it since its apart of the air. Condensation is what makes water vapor visible.

Basically high temperatures excite water molecules until they change from a liquid state to a gaseous one. However lower temperatures can cause enough water vapor to condense back into liquid form. This small amount stays as very small droplets that can stay suspended in the air mostly thanks to small dust particles that they attach themselves to.

It is pretty much the same way you see small bits of glitter suspended in clear glue. The drops are small enough to stay trapped in the air until condensation reaches a point of no return making rain. One result of this is that light becomes reflected and refracted. This is what makes clouds visible.

Now if you think about it we also just answered the second question about why clouds last so long. You may understand the first explanation because you can see your breath on a cold day. However after a while depending on the weather you notice that later in the day you can no longer see your breath. Clouds are visible because of colder temperatures in the upper atmosphere.

You have to remember that in the upper reaches of the atmosphere that the temperatures are much colder. This means that water vapor once condensed can no longer return fully to its gas state. Since temperatures don’t change in this region clouds are able to keep shape longer.

Finally, clouds have color. Some are white, some are grey, and in special circumstances such as major storms can have weird colors like green or red. This goes back to refraction. Most color that we can see is visible because are eyes perceive how objects absorb or reflect certain wavelengths of light. The white colors of clouds come from the condensed water vapor having a high reflective quality.

When all wavelengths of light are reflected back you see white. The grey color comes from seeing clouds from beneath. White clouds are white if you notice, on sunny days. This is because you can see the sunlight directly hitting them and see that light almost completely reflected back. On cloudy days most sunlight is blocked by the translucent and refractive quality of cloud cover. This makes clouds appear darker in color as part of the light has been uniformly absorbed.

We have written many articles about clouds for Universe Today. Here’s an article about the types of clouds, and here’s an article about cirrocumulus clouds.

If you’d like more info on clouds, check out an article aboutClouds. And here’s a link to NASA Spaceplace Page about Clouds.

We’ve also recorded an episode of Astronomy Cast all about the Atmosphere. Listen here, Episode 151: Atmospheres.

Posted on by Jon Voisey

Does Tidal Evolution Cause Stars to Eat Planets?

Artists impression of the 'hot Jupiter' HD209458b, which has incredible storms. Credit: ESO.

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With the success of the Kepler mission, the viability of looking for planets via transits has reached maturity. However, Kepler is not the first intensive study. Previously, other observatories have employed transit searches. To increase the chances of discovery, studies often concentrated on large clusters in which thousands of stars could be observed simultaneously. Based on the percentage of stars with super Jovian planets in the Sun’s vicinity, a Hubble observation run on the globular cluster 47 Tuc expected to find roughly 17 “hot Jupiters”. Yet not a single one was found. Follow-up studies on other regions of 47 Tuc, published in 2005, also reported a similar lack of signals.

Could the subtle effect of tidal forces have caused the planets to be consumed by their parent stars?

Within our solar system, the effects of tidal influences are more subtle than planetary destruction. But on stars with massive planets in tight orbits, the effects can be very different. As a planet would orbit its parent star, its gravitational pull would pull the star’s photosphere towards it. In a frictionless environment, the raised bulge would remain directly under the planet. Since the real world has real friction, the bulge will be displaced.

If the star rotates slower than the planet orbits (a likely scenario for close in planets since stars slow themselves via magnetic breaking during formation), the bulge will trail behind the planet since the pull has to compete against the photospheric material through which its pulling. This is the same effect that happens between the Earth-Moon system and is why we don’t have tides whenever the moon is overhead, but rather, the tides occur some time later. This lagging bulge creates a component of the gravitational force opposed to the direction of motion of the planet, slowing it down. As time goes on, the planet gets dragged closer to the star by this torque which increases the gravitational force and accelerating the process until the planet eventually enters the star’s photosphere.

Since transit discoveries rely on the planets orbital plane being exactly in line with its parent star and our planet, this favors planets in a very tight orbit since planets further out are more likely to pass above or below their parent star when viewed from Earth. The result of this is that planets that could potentially be discovered by this method are especially prone to this tidal slowing and destruction. This effect with the combination of the old age of 47 Tuc, may explain the dearth of discoveries.

Using a Monte-Carlo simulation, a recent paper explores this possibility and finds that, with the tidal effects, the non-detection in 47 Tuc is completely accounted for without the need to include additional reasons (such as metal deficiency in the cluster). However, to go beyond simply explaining a null result, the team made several predictions that would serve to confirm the destruction of such planets. If a planet were wholly consumed, the heavier elements should be present in the atmospheres of their parent star and thus be detectable via their spectra in contrast with the overall chemical composition of the cluster. Planets that were tidally stripped of atmospheres by filling their Roche Lobes could still be detected as an excess of rocky, super Earths.

Another test could inolve comparison between several of the open clusters visible in the Kepler study. Should astronomers find a decrease in the probability of finding hot Jupiters corresponding with a decrease with cluster age, this would also confirm the hypothesis. Since several such clusters exist within the area planned for the Kepler survey, this option is the most readily accessible. Ultimately, this result make sit clear that, should astronomers rely on methods that are best suited for short period planets, they may need to expand their observation window sufficiently since planets with a sufficiently short period may be prone to being consumed.

Posted on by Tega Jessa

What are Electrons

Fine Structure Constant

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If you have heard of electrons you know that they have something to do with electricity and atoms. If so you are mostly right in describing what are electrons. Electrons are the subatomic particles that orbit the nucleus of an atom. They are generally negative in charge and are much smaller than the nucleus of the atom. If you wanted a proper size comparison the size of the earth in comparison to the sun would be a pretty close visualization.

Electrons are known to fall into orbits or energy levels. These orbits are not visible paths like the orbit of a planet or celestial body. The reason is that atoms are notoriously small and the best microscopes can only view so much of atoms at that scale. Even if we could view electrons they would move too fast for the human eye. As a matter of fact scientists still can’t calculate the exact position of electrons. They can only estimate their locations. That is why the modern model of the atoms has an electron cloud surrounding the nucleus of an atom instead of a defined system of electrons in concentric orbits.

Electrons are also important for the bonding of individual atoms together. With out this bonding force between atoms matter would not be able to interact in the many reactions and forms we see every day. This interaction between the outer electron layers of an atom is call atomic bonding. It can occur in two forms. One is covalent bonding where atoms share electrons in their outer orbits. The other is ionic bonding where an atom gives up electrons to another atom. In either case bonding must meet specific rules. We won’t go into great detail, but each electron orbit or electron energy level can only hold so many electrons. Atoms can only bond if there is room to share or receive extra electrons on the outermost orbit of the atom.

Electrons are also important to electricity. Electricity is basically the exchange of electrons in a stream called a current through a conducting medium. In most cases the medium is an acid, metal, or similar conductor. In the case of static electricity, a stream of electrons travels through the medium of air.

The understanding of the electron has allowed for a better understanding of some of the most important forces in our universe such as the electromagnetic force. Understanding its workings has allowed scientist to work out concepts such potential difference and the relationship between electrical and magnetic fields.

We have written many articles about electrons for Universe Today. Here’s an article about the atom diagram, and here’s an article about the electron cloud model.

If you’d like more info on Electrons, check out the Discussion about Electrons, and here’s a link to the History of the Electron Article.

We’ve also recorded an entire episode of Astronomy Cast all about the Atom. Listen here, Episode 164: Inside the Atom.

Sources:
Wikipedia
Windows to Universe