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Roger Abella Queralt (DeMS)
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Roger Abella Queralt

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Does the Universe Have a Center?

We like to think that everything has a starting point—that everything has a beginning, middle, and end. If this view is accurate, then the universe must have a center. This understanding of the cosmos makes things simple to grasp, but unfortunately, it’s also terribly inaccurate.

So, what's the truth of the matter? Does the universe have a center? See: http://goo.gl/UdbYzZ

Image (artistic rendering of the Milky Way Galaxy) Credit: NASA
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Loop de Loop

Last month research project known as BICEP2 announced evidence of inflation within the cosmic microwave background (CMB). Now a new paper argues that a different effect known as a radio loop could produce similar results, which raises the question of whether inflation was detected after all.

The evidence for inflation focused on what is known as B-mode polarization of the CMB.  The B-mode polarization has two causes.  The first is due to gravitational lensing.  The cosmic microwave background we see today has travelled for more than 13 billion years before reaching us.  Along its journey some of it has passed close enough to galaxies and the like to be gravitationally lensed.  This gravitational lensing twists the polarization a bit, giving some of it a B-mode polarization. The second mechanism which is more subtle, and requires more data to analyze. It is due to gravitational waves produced during the inflationary period of the big bang.  What the BICEP2 found was evidence of more B-mode polarization than expected by gravitational lensing alone.  Since there are two ways in which B-mode polarization can occur, they needed to show that this “extra” was not just due to lensing.  Thus, they argued, it must be due to primordial gravitational waves.

This new paper looks at another possible source known as radio loops. A radio loop is caused by large magnetic fields that span interstellar space.  When ionized plasma interacts with these magnetic fields, the charged particles spiral along the magnetic field. The spiraling charges then emit radio waves through what is known as synchrotron radiation.  As a result, radio waves are emitted all along the magnetic field loop, hence a “radio loop.”

But the authors point out that these loops can also produce microwave radiation, emitted by charged dust particles within the plasma.  These microwave emissions are in the same wavelength range as the cosmic microwave background.  The emissions are polarized, and their orientation would be similar to the B-mode polarization detected by BICEP2.

Once this “foreground effect” of galactic radio loops is accounted for, there may still be a residual B-mode evidence of inflation.  At this point we can’t be sure because it wasn’t taken into account in the BICEP2 results. What this new paper really points out is a weakness in the BICEP2 results, specifically that it was done at a single wavelength range.

The real test will happen when the Planck team releases their results on B-mode polarization.  The Planck satellite has polarization data at multiple wavelengths.  If these results confirm BICEP2, then we can be sure of an inflationary effect.  If not, then we’ve got more work to do.  And so it goes, loop de loop, back and forth.

This is how science is done.  One team puts forward a result, other teams push back with other ideas, and eventually the best result survives.

Image: Galactic radio loops, with BICEP2 region indicated. Credit: Philipp Mertsch

Paper: Hao Liu, Philipp Mertsch, and Subir Sarkar. Fingerprints of Galactic Loop I on the Cosmic Microwave Background. arXiv:1404.1899 [astro-ph.CO] (2014).
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As seen on #Cosmos: Our Sun

On August 31, 2012 a long filament of solar material that had been hovering in the sun's atmosphere, the corona, erupted out into space at 4:36 p.m. EDT. The coronal mass ejection, or CME, traveled at over 900 miles per second. The CME did not travel directly toward Earth, but did connect with Earth's magnetic environment, or magnetosphere, causing aurora to appear on the night of Monday, September 3.

The image above includes an image of Earth to show the size of the CME compared to the size of Earth.

Credit: NASA/GSFC/SDO
#sun #solar #solarsystem #sdo #nasa #space

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Roger Abella Queralt

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Black Holes: So You CAN Divide By Zero

“Black holes are where God (or the Flying Spaghetti monster, maybe) divided by zero.” That has to be one of my favorite math/science jokes. Surprisingly enough, weird things do happen to our equations when you work inside the event horizon of black holes – such as dividing everything by zero. So, other than being the source of a great joke, what are black holes?

Learn more about black holes and how they were discovered at:
http://www.fromquarkstoquasars.com/black-holes-so-you-can-divide-by-zero/

Image source:
http://www.huffingtonpost.com/2013/04/08/black-hole-firewall-theory-paradox-einstein-equivalence_n_3036733.html
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Star Dates

Determining the age of a star poses a bit of a challenge for astronomers. After all, stars exist over a timescale of billions of years, and they are light years away.  We can’t use radiometric dating like we do for rocks and other objects on Earth.  So just how do we determine the age of a star? It turns out that there are several ways, and it’s getting easier to do.

One of the ways is to compare a star’s mass with its brightness (absolute magnitude).  We can determine the mass of a star if it is part of a binary system, and if we have a good measure of its distance (say, through its parallax) then we can observe its apparent magnitude and use its distance to determine its absolute magnitude.  The way we determine its age is by recognizing that main sequence stars grow hotter and brighter over time.  Stars produce light and heat through nuclear fusion in their core.  As more hydrogen fuses into helium, the fusion rates gradually increase, producing more heat and light.  So for stars of a particular mass, brighter stars are older than dimmer stars.  By observing stars that are newly formed and stars at the end of their life we have an idea of the rate at which stars brighten over time, so we can get a measure of a star’s age.

Another way is to measure a star’s rate of rotation.  For stars around a solar mass or less, the rate of rotation of a star gradually decreases.  So the rotation rate of a star depends upon its mass and age.  By measuring the rotation of a star and comparing it to the rotation of the Sun (for which we know its age very well), we can determine its age.

There are a few downsides with these age measurements.  For one, they only work with main sequence stars, so very young and very old stars need to be studied with different measures.  For another, they depend upon measurements that have traditionally been challenging to do well.  But a new method presented in the Astrophysical Journal could provide an easier and more effective way to determine stellar ages.

The method uses what is known as helioseismology, which is the study of sonic oscillations within a star.  Helioseismology has long been used to study the interior structure of the Sun, but more recently it can also be used with stars.  Since the frequency of sound oscillations depends upon the mass and density of a star, helioseismology can be used to determine the mass and radius of a star pretty effectively.  Knowing that, one can use observations of a star’s spectrum to determine its temperature.  The mass, radius and temperature of a star can then be used to determine its age.

What makes this new method potentially powerful is that it depends upon the type of observational data gathered by sky surveys.  This initial study looked at about a thousand stars.  A larger project known as the Stroemgren survey for Asteroseismology and Galactic Archaeology (SAGA) is analyzing data gathered by the Kepler telescope.  Future observations by telescopes such as GAIA could provide a large survey of stellar ages within our galaxy.

The reason why this is important is that knowing the age of a large number of stars allows us to study the history of our galaxy.  By analyzing stellar ages, we can determine when star production was common, and when it was rare.  We might even be able to determine past collisions with our galaxy, which tend to drive star production.  This new method is still young, so it will take time to determine if it lives up to its potential.  But if it does we may soon gain deeper understanding of the history of our galaxy.

Paper:  L. Casagrande, et al. Stroemgren survey for Asteroseismology and Galactic Archaeology: let the SAGA begin.  L. Casagrande, et al. arXiv:1403.2754 (2014)
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Roger Abella Queralt

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Mouseover text;
" Last week, we busted the myth that electroweak gauge symmetry is broken by the Higgs mechanism.  We'll also examine the existence of God and whether true love exists. "
http://xkcd.com/397/

h/t +Bob Schlette 
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Yup, I guess he was only using it to illustrate his point.
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Roger Abella Queralt

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Pivoting planets that lean one way and then change orientation within a short geological time period might be surprisingly habitable, according to new modeling.

The climate effects generated on these wobbling worlds could prevent them from turning into glacier-covered ice lockers, even if those planets are somewhat far from their stars. And with some water remaining liquid on the surface long-term, such planets could maintain favorable conditions for life. Fore more information, visit: http://go.nasa.gov/1nquyFz 
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Blood Moon

This week those of us in the western hemisphere will have the chance to observe a lunar eclipse.  It will happen in the evening/morning of April 14/15, reaching peak darkness at about 3 a.m. EDT (0600 GMT).  Depending on the darkness of your sky, the Moon may be invisible to the naked eye, or it may appear as a dark, blood moon.

A lunar eclipse occurs when the Moon passes through the shadow of the Earth.  For this reason, lunar eclipses occur when the Moon is in its full phase.  Given that the Moon orbits the Earth, you might wonder why there isn’t a lunar eclipse every month.  If the orbit of the Moon were exactly in line with the orbit of the Sun, then that is exactly what would happen. But the Moon’s orbit is tilted about five degrees relative to the orbit of Earth, and this means that the Moon is often slightly above or below the Earth’s shadow when it passes through its full phase. So most months there is no lunar eclipse.

For the Moon to be lined up in the right way, it has to be located near the plane of the Earth’s orbit when it passes behind the Earth, and this only happens twice a year, about 6 months apart. This is why there are “eclipse seasons” in Spring and Fall. There are at least two lunar eclipses each year, but there can be as many as 5.

Not all lunar eclipses are alike. As seen in the image below, since the Sun is larger than the Earth, there are regions where only part of the Sun is blocked by the Earth, and the resulting shadow is called the penumbra. For a much smaller region where the Sun is completely blocked by the Earth, the shadow is called the umbra. The type of eclipse that occurs depends on whether the Moon passes through umbra or penumbra.

If the Moon just passes through penumbra, then what occurs is a partial lunar eclipse.  In this case only part of the moon will appear dimmed.  If the Moon passes through the umbra, then you get a total lunar eclipse.  It is while passing through the umbra that you can observe a blood Moon.  The reason the Moon can appear red rather than completely dark is that some sunlight is refracted by the Earth’s atmosphere.  If you were standing on the Moon during a lunar eclipse you would see the Earth surrounded by a ring of sunset.

This particular lunar eclipse is a total one, and it marks the first of four consecutive total lunar eclipses.  One for each eclipse season every six months.  So if you miss this one, you’ll have another three chances over the next year and a half.  After that, total lunar eclipses will be less common for a while.

So brace yourselves, the eclipses are coming. 

Image: Schematic of a lunar eclipse. Credit: Wikipedia
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A map of our galaxy the Milky Way, showing pulsars (red), planetary nebulae (blue), globular clusters (yellow), and the orbits of several stars.
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This is really cool! Thank you for sharing!!
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Siblings

Stars don’t form alone.  They form as part of a stellar nursery.  We know this because we can see new stars forming in this way, such as in the Orion nebula.  This means, of course, that our own Sun also formed in a stellar nursery with lots of other stars.  There are stars out in the galaxy that are siblings to our Sun, and we think we know where a few of them are.

You might think stars close to the Sun, like Alpha Centauri, are likely siblings, but that turns out not to be the case.  The Sun formed about 5 billion years ago, and stars of a stellar nursery tend to disperse in random directions, so many of the Sun’s siblings are likely quite far away.  But it is possible that some solar siblings are relatively close.  If we assume that the Sun’s stellar nursery formed about 1,000 stars (which seems somewhat typical), then by one estimate about 10 siblings would be within 400 light years of the Sun, and about 100 within 4000 light years.  Other studies argue this might be too optimistic, but it at least seems feasible that a handful of solar siblings could be relatively close by.

Of course the trick is to identify them.  To be a candidate sibling, a star needs to satisfy three conditions.  First, it must be of similar age to the Sun.  Second, it must have a similar metallicity, meaning the ratio of various elements (relative to hydrogen and helium) must be similar to the ratio found in the Sun.  Third, it must have a trajectory that would allow it to have been in a similar region of the Sun 5 billion years ago.

This would seem to be more difficult than finding a needle in a haystack, but with large sky surveys the task is somewhat more tractable.  As outlined in a recent paper in Astronomy and Astrophysics, we now have five candidate siblings, including one found by this team.

The team searched through HARPS data to find candidate stars.  HARPS (High Accuracy Radial-velocity Planet Searcher) was a projected designed to look for exoplanets by measuring the wobble of the parent star, but to measure that wobble (radial velocity) you need a precise measurement of a stars spectrum.  The team analyzed the spectrum to determine the metallicity and age of more than a thousand stars.  The HARPS data also provided information on the trajectories of these stars.  From this they were able to discover a new candidate sibling.

As we make larger and more precise surveys of the Milky Way, such as the one planned for the Gaia satellite, we are likely to find even more siblings of our Sun.  This will help us further understand just how our Sun came to be.

Image: Drift of siblings in the galaxy. Credit: Don Dixon.
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