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Brian Koberlein
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Brian Koberlein

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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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When will the next ' loop de loop' study occur?
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Dark Star

Although still mysterious, dark matter is five times more plentiful than regular matter in the universe.  It affects the formation and clustering of galaxies, as well as the motion of stars through their galaxy.  So it is tempting to wonder what effect dark matter might have on the formation and evolution of stars themselves.  The problem is we can’t be sure without an understanding of type of dark matter which exists.  That hasn’t stopped some astronomers from speculating, however.

One idea is that dark matter could accumulate in the core of stars. Given the current estimated density of dark matter around stars like the Sun, this wouldn’t have a significant effect, but if the density were about 200 times more dense, and if dark matter is a type known as asymmetric dark matter (ADM) then it could affect the brightness of stars, particularly those sun-sized or smaller.

One of the ideas about dark matter is that it is likely made up of some yet-unknown type of particles (WIMPs).  Just as regular matter particles have corresponding anti-matter particles, dark matter particles could also have anti-matter siblings. Asymmetric dark matter is a hypothetical type of dark matter where there is an asymmetry between regular dark matter and anti-dark matter.  This would mean that the two types wouldn’t annihilate each other very effectively, so the type of gamma ray signal some astronomers have looked for (and might have found) wouldn’t be very strong.

But such ADM would interact with the nuclear reactions inside the core of a star.  As a result of these interactions, fusion would occur more efficiently, and therefore the star would produce more light and heat than expected.  For large stars, this extra boost would be small compared to the pure matter rate, but for smaller stars (particularly red dwarf stars) this extra boost could be significant.  As a result, small stars could be brighter and hotter than expected.

We think dark matter would have a higher density around the core of a galaxy.  So the density of dark matter in that region might be high enough to have a measurable impact on stellar fusion.  If that’s the case, then we should be able to observe red dwarf stars near galactic center that are hotter and brighter than their mass predicts.  Observing such red dwarf stars in our own galactic core would be difficult because of all the gas and dust in that region, but perhaps such an effect could be observed in other galaxies.

Just to be  clear, this is still pretty speculative.  Dark matter remains a big mystery, and it might not be ADM.  But it is good to develop these types of models to determine what effects there might be.  That way if we start seeing these effects they can lead us to the correct model.

Paper:  Ilídio Lopes and Joseph Silk. A Particle Dark Matter Footprint on the First Generation of Stars. ApJ 786 25. (2014)

Paper: Fabio Iocco, et al.  Main Sequence Stars with Asymmetric Dark Matter. Physical Review Letters 108, 061301 (2012)
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who can say that this marvel was not created by an intelligent creator but came about  by chance let him prove it?
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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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Nice post, earths shadow always give more depth to the moon as it did last night.
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Money for Nothing

Although there is a great deal of evidence for the big bang, it does raise an interesting question.  If the universe began with the big bang, what caused the big bang? That’s a bit of a stumper, because we aren’t entirely sure.  Observationally, we have a good understanding of the universe as far back as nucleosynthesis, which occurred when the universe was about 10 seconds old.  We also have some initial observational evidence of the inflationary period, which occurred in the earliest moments of the universe.    As for the cause of the universe, we just have ideas at this point.  One of the more popular ones is that the universe quite literally came from nothing.

The “nothing” in this case is not the type of nothing we might typically imagine. Here, “nothing” refers to the idea that there are no particles, energy, space, or anything else that could be considered “real” in a traditional sense.  Instead there is only a quantum potential, or a nebulous cosmic wavefunction.  You might argue that a quantum state subject to some set of physical laws is hardly “nothing”, and I’d be inclined to agree with you, but in cosmology the term “nothing” has kind of stuck.  It’s similar to the term “big bang” being used for an event that was neither big nor explosive.

That said, there has been some interesting theoretical work on just what this quantum nothing might have been like.  One such work was recently published in Physical Review D. In this paper the authors looked at what is known as the Wheeler-DeWitt equation, which is a way to describe the entire universe within the framework of quantum mechanics.  The model is not without its problems, but it is a way to study the intersection between general relativity (gravity) and quantum theory.

Within the Wheeler-DeWitt formalism, it is possible for quantum fluctuations to occur.  Basically, within the quantum nothing fluctuations of spacetime can appear, though they would dissolve back into the quantum-ness. The team showed that in certain cases it is possible for such a fluctuation to expand rapidly, where the state of the quantum system acts as a cosmological constant to cause inflation.  Once that occurs, the fluctuation is to big to dissolve back into a quantum state, and has thus become “real”.  What this shows is that it is possible for a quantum state to give rise to a universe with an early inflationary period, similar to the way our universe seemed to arise.

It should be kept in mind that this is still very speculative.  This work is really a demonstration of a possibility, and not confirmation of how our universe came to be.  We are only beginning to gather evidence on the inflationary period of the big bang, and we’ll need a solid understanding of that period before we can explore any quantum origin of the Cosmos.

In the end, these ideas might prove successful, or it may turn out that nothing comes of it.

Paper: Dongshan He, Dongfeng Gao, and Qing-yu Cai. Spontaneous creation of the universe from nothing.  Phys. Rev. D 89, 083510 (2014)
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We will not get far unless we yield to a higher power. food for thought.
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Sunrise, Sunset

Yesterday on Reddit, a user named SipTime posted two images.  One of sunrise in Florida, and another of sunset in Japan.  The two photos were taken within minutes of each other. Sunrise and sunset at the same time.

Since we live on a small rocky sphere, this happens all the time. While the sun rises on one end of the planet, it sets on the other.  Between these two points it is either noon or midnight.  As the Earth turns, we move in and out of the shadow of our world. The Sun appears to rise and set as the Earth rotates upon its axis.

Of course we know that both are the same Sun.  Since the Sun is about 150 million kilometers away, the light must travel for more than 8 minutes to reach us.  All that distance and time, just to reach Earth.  If it had traveled in a slightly different direction, it would have missed the Earth entirely. The Earth is only 12,700 kilometers wide, so the light of sunrise and sunset left the Sun in almost the same direction. A difference in direction of only 0.4% of a degree (18 seconds of arc) is enough to separated morning sunlight from evening.

So not only are these the same Sun, they are almost the same light.

We live on a small rock racing through space.  And our days are marked by the rising and setting of a star.

Image: From Reddit user SipTime, used with permission.
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+Shane Corbett - Thank my parents.  That's where I learned it.
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Have him in circles
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Brian Koberlein

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When our Sun reaches the end of its life, it will enter a period of variable brightness.  Such as star is known as a Mira variable, and there are several that we can observe oscillating in brightness over the years.
Mira is a red star in the constellation Cetus. It is a variable star, meaning that its brightness changes over time. The name Mira is Latin for “wondrous”, and so Mira is indeed a wondrous star.
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Great relatable description of Mira star life and variables. Thankyou, David
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When we use parallax to determine stellar distances, we actually determine the distance relative to the distance of Earth from the Sun, what is known as an astronomical unit.  How do we know what an astronomical unit is?  We've had a basic idea for a long time, but it wasn't until a transit of Venus that we determined it precisely.
Thanks to a rare alignment of planets 250 years ago, we were able to learn for the first time just how large our solar system really is.
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Would a transit from Mercury could have served as well? Or is the planet so small that it was impossible to distinguish during transits?
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How is it that we can say with confidence that a particular star is 120 light years away?  It has to do with an effect known as parallax.
How is it possible to say with confidence that one star is 8 light-years away, while another is 640 light-years away? There are actually several methods to determine cosmic distances, and these are combined to create what is known as the cosmic distance ladder, but the oldest and most direct method uses the property of parallax.
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Here's a little (OK, it's long) video I produced a year ago that touches heavily on parallax astronomy: http://vimeo.com/58019825
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Just how many planets in the universe hold the potential for life?  We aren't sure at this point.  We do, however, know enough about exoplanets that we can make a pretty good estimation of just how many planets exist in the habitable zone of their sun.  This region is sometimes referred to as the "Goldilocks Zone."
Earth is the one planet we know of that is well suited for life. Of course this is a sample size of only one, and it’s a biased sample, since we’re it. This means we should take any speculation on the existence of life on other planets with a grain of salt, but there are some things we can at least tentatively speculate on.
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+Bill Davidsen Thanks for the clarification.
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Look up at the night sky, and you see the history of the universe.  That's because light takes time to reach us.  Some stars are fairly close, and the light only takes a few years to come to our doorstep.  Other objects are farther away, and began their journey almost at the beginning of time.
When you look up into the night sky, you are seeing into the past. Cosmic distances are so vast that it takes time for light to travel them. The brightest star in the night sky is Sirius, more than 8 light-years away, which means we see Sirius not as it is now, but as it was 8 years ago.
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+Brian Koberlein what lies beyond the farthest stars? How large is the universe?

Interesting read as usual
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Have him in circles
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Astrophysicist, Professor, Author
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An astrophysicist and physics professor at Rochester Institute of Technology.  Author of "Astrophysics Through Computation" with David Meisel.  Creator of the science outreach project Prove Your World, developing a science television show for children.

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