Podcaster: Morgan Rehnberg

Title:   Monthly News Roundup – Galaxies Galore!

Link :

Magellanic Stream:
Quenched galaxies:
Stellar convection:

Description: In this episode of the Monthly News Roundup, we discover new information about galaxies near and far.  A new technique allows us to better understand stars thanks to the search for planets.  A bright explosion can be seen in the sky, and Curiosity has a bright future after only a year on Mars.

Bio: Morgan Rehnberg is a graduate student in astrophysics and planetary science at the University of Colorado – Boulder.  When not studying the rings of Saturn, he develops software to help search for asteroids that might hit the Earth.  He blogs and podcasts about astronomy and space science at

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2013, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at



You’re listening to the 365 Days of Astronomy podcast for August 31st, 2013.  I’m Morgan Rehnberg and this is the Monthly News Roundup.  This episode was produced by Cosmic Chatter and recorded August 25th from Boulder, Colorado.


Let’s start this month with the resolution to a galactic mystery.  If you look up at the night sky from somewhere dark, it’s impossible to miss the Milky Way.  Our galaxy stretches brilliantly across the sky, containing hundreds of billions of stars.  If you happen to be in the southern hemisphere, however, something else might catch your eye.  Two other bright smears in the sky mark the location of the Large and Small Magellanic Clouds.  These clouds are actually small galaxies being pulled in by the gravity of the Milky Way.  They are only a couple hundred thousand lightyears away – practically on our doorstep in cosmic terms!

What you can’t see with your naked eye is that the Magellanic Clouds are really only the tip of a stream of gas that stretches nearly two-thirds of the way around our galaxy.  Called the Magellanic Stream, this gas has been stripped away from the dwarf galaxies as they approach our own.  But which galaxy did this gas come from?

The traditional thought has been that most of it comes from the closer, smaller galaxy – an idea backed up by previous observations.  New observations, however, suggest that more recently stripped gas originates from the larger one.  The Large Magellanic Cloud is just coming into contact with the envelope of hot gas which surrounds the Milky Way.  This interaction pulls the gas away and into the Magellanic Stream.

By better understanding this process, we can more accurately predict the breakup of the Clouds, which will probably eventually merge with the Milky Way.


Let’s look at another aspect in the life of a galaxy.  Galaxies like our own have been making new stars for billions of years and continue to do so today.  As old stars die, they provide fresh life to the galaxy.  Some galaxies, however, eventually stop this production.  Astronomers call these “quenched galaxies.”

The farther a galaxy is from us, the earlier in the history of the universe we are viewing it.  If we look at the quenched galaxies in the early universe, they appear far smaller than those seen today.  Why this is has been an open question in the field of galaxy evolution.

One popular theory is that today’s larger quenched galaxies are simply the result of two smaller ones merging.  Since we’ve observed plenty of other galactic mergers, this seems pretty reasonable.  New research released this month, however, says that this is not the case.

Astronomers observed a region of sky and studied galaxies over the course of eight billion years of evolution.  They did not observe these quenched mergers.  Instead, they propose that modern quenched galaxies are larger because they started with more star-forming material.  This allowed them to grow in size beyond their ancestors before exhausting their gas and dust.


Earlier this month, NASA officially ended rescue work on the Kepler Space Telescope.  Operational since 2010, Kepler has identified thousands of potential planets outside our solar system.  But that’s not its only contribution to astronomy.  Lesser known is that it has also provided high-precision light curves for over 150,000 stars in our galaxy.  A light curve is simply a measure of how a star’s brightness changes with time.

This month, a team of astronomers announced an exciting new way to use this data.  They show that a star’s light curve can be used to predict its surface gravity, an important attribute.  Combined with a star’s temperature, which can be measured from the color of its light, surface gravity allows for accurate calculation of many stellar properties.

How does this work? Stars are hottest at their core and coolest at their surface.  Just like convection in your oven, hot material from below rises to the top, where it cools.  Hotter material is brighter than cooler material, so this process causes the star to flicker subtly, which can be observed in the light curve.  Of course, there are many other things which also cause changes in brightness.  Sunspots, for example, make this a more challenging measurement to make.

Because of this, highly accurate light curves are required.  Until another telescope like Kepler is able to patiently monitor hundreds of thousands of stars, this technique will be of limited use.  But with more than one hundred thousand stars already monitored, it’s poised to change our understanding of stars as we know them.


August marked an unusual chance to view a powerful stellar explosion.  Look high in the night sky and you may catch a glimpse of a powerful nova.  This is the brightest nova as seen from Earth since 2007.  Even so, it will only look like a moderately bright star to the naked eye.

Novae occur under an unusual set of circumstances.  They originate with a binary star system, where two stars orbit each other.  When one of the stars reaches the end of its life, it ejects its outer layers to become a white dwarf.  If the other star orbits close enough, some of its material may fall onto the white dwarf.  This material builds up on the surface until the pressure becomes too great.  The surface ignites in a tremendous nuclear explosion called a nova.

This explosion throws off most of the newly-acquired material.  Each time a nova occurs, however, a little is left behind.  Eventually the star grows  to a size called the Chandrasekhar limit.  At this point, the star is so large that it cannot support its own mass. It explodes in a violent type-1a supernova – one of the most powerful explosions in the Universe.

The 2011 Nobel Prize in Physics was awarded to scientists who used Type 1a Supernovae to confirm the accelerating expansion of our universe.  How quickly a type 1a supernova fades allows us to determine its intrinsic peak brightness, which scientists can use to determine how far away it is.  They found that supernovae in distant galaxies are dimmer than expected, indicating that the universe is expanding and pushing galaxies farther away from each other.


It’s hard to believe, but one year ago this August millions sat riveted as a hovering sky crane lowered the two billion dollar Mars Science Laboratory onto the surface of Mars.  It was a flawless landing, but how has Curiosity fared in the intervening year?  Pretty well, it turns out. Despite having to take a month off during Mars’ opposition with the Earth, Curiosity has accomplished a lot in the first half of its planned two-year mission.

Milestones thus far include exploring a riverbed, measuring the levels of solar radiation on the Martian surface, and drilling into the first rock on another world.  Curiosity has begun her journey to a nearby mountain; studying this location will dominate her second year on the surface of Mars.

But perhaps more important than the science she’s accomplished is the public image she’s created.  In a world haunted by budget cuts and a public that’s disinterested in science, this mission has returned NASA to it’s whiz-bang status of yore.  From its dramatic landing to its jaw-dropping self portraits, the rover has truly captured the public’s imagination.

But if Curiosity hopes to become NASA’s most successful rover, she still has a long ways to go.  Opportunity, launched in 2003, has been roving Mars for more than a decade.  For a mission designed to last just three months, it’s a remarkable success story and a testament to our ongoing success in space.


Thanks for listening to this episode of the Monthly News Roundup.  A special thanks this month to Vivienne Baldassare for contributing the story on novae.  For more astronomy news and commentary, visit or follow @cosmic_chatter on Twitter.  As always, you can send your comments and corrections to  See you in September!


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365 Days of Astronomy
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