Tuesday, March 26, 2013

The Birth of the Universe, through Today's Telescopes

by Sandra Ning, Terra Linda HS

A nebula in the Large Magellanic Cloud. Though nebulae are often the focus of space appreciation in pop culture, the universe encompasses billions more phenomena.

     A story is typically told from the beginning, but oftentimes the universe is an exception. As a society, time is measured in days and nights, hours, minutes, and seconds. But even more so, time is apparent to us through the peachy sunrise of dawn, the angry grumbles of an empty stomach at noon, and the fatigue that settles with the darkness of night. It's hard to imagine any of these things in relation to the universe, with its sleepless planets and nomadic asteroids, all swallowed up in an unimaginably large blanket of space. If the universe is a story, and all the galaxies, comets, and stars its characters, where does it all begin? 
     Luckily, scientists have already delved into the origins of the universe, and have resurfaced with new and exciting insights regarding these questions. Dr. Mary Barsony, an associate professor of physics and astronomy at SFSU, has kindly answered several questions regarding the birth of the universe, the elements, and how scientists are researching it all.--

1. The Big Bang theory is the most widely-accepted theory for the creation of the universe. What kind of evidence have astrophysicists gathered to support this?


    a) Apart from the "immediate" neighborhood of our Milky Way Galaxy,
in any direction you look, the further away a galaxy is, the greater the shift
of its spectral lines towards longer wavelengths (e.g., towards the red portion of the spectrum, hence the term "red-shifted.") This systematic red-shift of extragalactic spectra
was first discovered nearly a hundred years ago, by combining spectra obtained
by V.V. Slipher at Lowell Observatory with distance determinations obtained by
E. Hubble at Mt. Wilson Observatory. 


           Any cosmological theory must explain this observational fact. According
to the Big Bang theory, the observed red-shifts are a direct consequence of
the expansion of the Universe since the Big Bang (13.7 billion years ago).
As space(time) expands, the light-waves stretch with the space they are in,
meaning their wavelengths get longer, or red-shifted.


 Timeline of the universe, showing the formation of particles, then nebula, then more.


     b) There is remnant radiation observed in all directions of space, corresponding
to a temperature of 2.73 Kelvins (above absolute zero), peaking at a wavelength of
~1 millimeter, which is in the "microwave" region of the electromagnetic spectrum.


         Any cosmological theory must explain why we see this radiation uniformly
in all directions in the sky.  According to the Big Bang theory, early in the
Universe's history, its state was extremely hot and dense--so hot that
protons and electrons were separated from each other in a state
known as a "plasma." Photons (light) cannot escape such a plasma,
since photons strongly interact with free electrons and protons. This
interaction is called "scattering."  As the Universe expands, it cools. Once the Universe
had expanded and cooled enough so that protons and electrons
could combine to form atoms, the plasma turned into an electrically
neutral state, and the photons could escape--so instead of a dense, opaque
fog of scattered photons, we have a transparent state of freely propagating photons (light).
The microwave background radiation was discovered (accidentally) by some radio
communications engineers (as a source of unwanted noise in their communications
equipment). They received the Nobel Prize in Physics for their discovery.


    c)  We observe the elemental abundances in the Universe to be
~90% (by number) hydrogen and ~10% (by number) helium.
In terms of mass, this corresponds to ~75% by mass of hydrogen and ~24% by mass
helium. All the other elements we are familiar with here on Earth are trace
elements relative to these, on the scale of stars, galaxies, and galaxy clusters.


      The abundances of hydrogen and helium are predicted by the Big Bang theory
in terms of what is known as "Big Bang nucleosynthesis."


2. Did all of the elements form at once with the Big Bang? And if not, in what order (if any) did they form in?


      The nucleon formation order in the Big Bang was: protons (protons are nuclei
of hydrogen) and neutrons, then deuterons (the nuclei of deuterium or heavy
water), then helium nuclei (both "light" helium, with  2 protons+1 neutron and "regular" helium, with 2 protons + 2 neutrons), then lithium. All the tritium nuclei (12 yr half-life) and beryllium nuclei (53 day half-life) formed in the Big Bang decayed into deuterons or lithium.
  
          All other elements are formed either within massive stars, post-main-sequence stars, supernovae, or spallation of cosmic particles and interstellar hydrogen nuclei (protons).


3. Would it be theoretically possible to create even more elements?


       Yes, elements past uranium, the so-called "trans-uranium" elements
are all formed in the lab with accelerators. Generally, these very heavy
elements are unstable and decay (their nuclei split apart, or undergo "fission")
in fractions of a second.


4. What elements are "stardust" and nebulae primarily composed of? 


    Interstellar dust is mainly composed of silicates and hydrocarbons.


     Nebulae are generally gas lit up by a nearby light source, which could be
a massive star or star cluster (e.g., Orion nebula) , a white dwarf (planetary
nebulae), a pulsar (Crab nebula), or very young star  (L1551 in Taurus).
Interstellar gas is primarily composed of hydrogen and helium, with  traces of
other, heavier elements.


A flowchart of star formation; protostars aren't shown in this chart, but would be between the stellar nebula and a fully-formed star.


6. What are neutron stars?

       A neutron star is an object made entirely of neutrons, that has a radius of ~10 km
and contains more than 1.4 solar masses.  Generally, it is a remnant of a
supernova explosion.

7.  And what are protostars?

       A protostar (of which I am one of the co-discoverers) is an object
which is still in the process of forming, with almost all of its mass residing
in an extended (~2000 Earth-Sun distances, or astronomical units) infalling envelope.
Its energy is derived from gravitational infall, and it fuels powerful bipolar
jets of gas, which act to remove its magnetic field and spin energy.


7. You're currently studying a protostar, the Wasp-Waist Nebula, right? What do scientists hope to learn from protostars, and for what purposes?


    Fantastic! You saw it! Yes, this nebula is mostly composed of hydrogen.
The protostar forming at the center of the Wasp-Waist Nebula may be the
first such object we have found that ultimately may form into a "failed star"
or "brown dwarf" (an object not massive enough to fuse hydrogen into helium
in its core) instead of into a low-mass star.


        We're hoping to understand, in detail, both how stars form from the
tenuous interstellar medium and how their planetary systems form.


The Wasp-Waist Nebula, which holds a protostar currently being studied.


8. Do orbiting planets form already orbiting a star? Or do they form, and then drift in space until a sizeable star is encountered?


     Actually, as stars form they form accretion disks, as well. Just like when
water goes down a drain, it generally swirls around before going down the center,
so gas and dust swirl around in a disk around the central protostar before falling in.
Planets eventually form from the disk orbiting the central young (pre-main-sequence,
or, not yet fusing hydrogen to helium) object.


9. Why are the outer planets all gas giants while the inner planets are all rock?


      That has to do with the temperature structure of the accretion disk
around a young, pre-main-sequence object. It's so hot close-in that only
rocky (silicates, iron) planets can form from planetesimals crashing into each other--it's too
hot for ices to form. Remember that, by far, most of the material in such
a disk is hydrogen, then helium, with just traces of heavier elements.


   Far enough out in the disk, the temperature cools enough so that both
ices (composed of water, carbon monoxide, ammonia) and rocks (silicates)
can form the central cores of planets. Once an icy/rocky core
surpasses about ten Earth masses, its gravitational pull can become
strong enough to hold onto and sweep up the disk's gas in and near its orbit.
This is how the gas giants Jupiter and Saturn, and the ice giants, Neptune and
Uranus, formed.


10. Is it difficult to study the formations of stars and planets? What obstacles are in the way of studying these formations?


       Yes, it's difficult, but it's rewarding. We are very lucky to live in the present
time, when our technology is allowing us to examine star and planet formation
in unprecedented detail.  The ALMA (Atacama Large Millimeter/submillimeter Array)
will revolutionize our understanding of this field.  This instrument (66 telescopes
working as one) was just inaugurated, on March 13, 2013.  https://science.nrao.edu


11. What kind of technology are scientists using to study these formations?


    Very many kinds. The ALMA array, for instance, uses the fastest, specially
made supercomputer (called a "correlator") to process the signals from
all of its antennas simultaneously every 10 seconds. The receivers for
detecting radiation from the sky are state-of-the-art and are approaching  (or at) the
quantum limit for how faint a signal they will respond to. Its data processing
software and user interface is brand new and continually being written and upgraded.
This is a truly international collaboration, with scientists from Europe,
North America, Taiwan, and Japan all equal partners in its use and development.


     For near-infrared arrays, to find new brown dwarfs
and young free-floating planets, we're using the largest such devices in existence.
For near-infrared spectroscopy, we're using a 400-fiber-optic fed
spectrograph (called FMOS) on the Subaru 8.0-meter telescope on Mauna Kea.
for a recent synopsis of this work).


     We're looking forward to JWST, the successor to Hubble, which will
work in the near- and mid-infrared. That is where we can study star and planet
formation much better than at optical wavelengths, where these objects
are generally invisible.


  12. How do SETI scientists try to find life in the universe?


  Currently, they are using the ATA (Allen Telescope Array),
looking in a specific frequency range (1-10 GHz) for
narrowband signals that might be transmitted by other


   SETI scientists are also studying geology, geophysics, atmospheric
science, and the conditions under which life may first have arisen on our own planet.
They are studying life in extreme environments on Earth, as in under the Antarctic
ice sheet and on the deep ocean floor where sunlight does not penetrate, and pressures
are high, etc.


13. You're very involved in different fields of astrophysics; how did you realize your interest in astronomy?

   I remember as a little girl of 4 or 5 years old, looking up at the dark sky, seeing the
stars, and wondering.

The night sky over the Church of Good Shepherd; New Zealand tried to get this patch of sky named a World Heritage Site.
 
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Come join the Marin Science Seminar during our Astronomy Month presentations! This Wednesday, March 27, Dr. Mary Barsony will be presenting 'We are Stardust: Genesis of the Elements'. The Marin Science Seminar takes place from 7:30 to 8:30 p.m., in rm. 207 of Terra Linda High School.

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Sandra Ning

Tuesday, March 12, 2013

Sinkholes in Space: Black Holes!

by Sandra Ning, Terra Linda HS    

 The first thing young students learn about space in their science classes is that it is huge. Earth becomes a speck in the solar system, infinitesimally small compared to the hulking gas giants orbiting ponderously outside of the asteroid belt, and infinitely distant from the roiling surface of the Sun. The solar system becomes a speck in the eye of the Milky Way galaxy: the heat of the Sun, too bright for humans to even look at, becomes mediocre in the face of thousands of other brighter, white-blue stars dotting the galaxy. Red dwarves overshadow even the largest planet, Jupiter. Even the harmonic system of the Sun and its orbiting planets is just one out of an incredible number of star clusters, constellations, distant planets and binary stars that comprise our galaxy.

      At the point when the solar system is only an afterthought on a distant arm of the Milky Way galaxy, and when the Milky Way becomes only one galaxy in an innumerable number within the universe, just about everyone begins to feel a little small.

      The good news is that there’s something smaller than little Earth and its inhabitants out in space. What might be considered bad news is that these innocuous little phenomena are the sucking, inescapable vortices of extreme gravitational pull that inevitably show up in every science-fiction novel: black holes.

An artist's depiction of a black hole 'devouring' a star, as the process is often called.

      The smallest black holes are thought to be as small as a marble, or even an atom. Yet, packed within black holes, is compressed, super-dense matter that results in a gravitational field around it that is so strong not even light can escape its grasp— hence the black hole’s invisibility in front of the searching eyes of telescopes.

      In actuality, the sizes of black holes fall into three categories: small, stellar, and supermassive. The smallest are thought to have formed during the birth of the universe, and pack literally tons of matter into areas that are very small. The result is, of course, the extreme density and gravitational field that characterize black holes.
      “Stellar” black holes are about the size of a star, and can be up to twenty times the size of the Sun. These black holes form when very large stars collapse and create a supernova explosion. Gravity and atomic forces are always at odds around any object in space. The mass of the object creates a gravitational pull that acts on the object, but the object’s core atomic and nuclear energy are often stronger and allow the object to resist being crushed by its own gravity. At times, though, massive stars near the end of their lifespan don’t have enough thermonuclear force to resist the incredible force of gravity their mass gives them.

Cassiopeia A, a young supernova in the Milky Way.

      The star thus collapses under the force of gravity, and explodes in what is known as a supernova. Bits of the star’s gases go flying in this spectacular event, creating the fire-like nebulae observatories sometimes capture in photos. The rest of the collapsing star gets crushed by gravity into an area smaller than the massive star, but a mass similar to that of the massive star.
      “Supermassive” black holes are, true to their name, incredibly large black holes that are often over one million times the size of the Sun. These black holes are, for reasons currently still being studied, found at the center of spiral galaxies; supermassive black holes are thought to be created around the same time the surrounding galaxy was formed. The supermassive black hole believed to be at the center of the Milky Way galaxy, known as Sagittarius A*, is as big as four million suns.

A picture taken of the Milky Way. Sagittarius A* is at the bottom right of the bright white cloud in the center.



      Black holes are not as sinister or dangerous as science fiction novels tend to suggest. Consider the universe as one, large fabric of ‘space-time,’ as Einstein imagined it. The Sun creates a sizable depression in the fabric with its mass, and the dip in the fabric is the gravitational pull that the orbiting planets around the Sun experience. Now, holding the same mass but with the volume of a penny, black holes are far smaller and far denser than the Sun. Placing one into the fabric of space-time creates a narrow, but deep depression in the fabric. This accounts for the inescapable gravitational force a black hole has. But outside of its narrow tunnel of gravitational pull, the fabric appears normal. In other words, gravity around a black hole is normal. Gravity only becomes an inescapable pull when matter passes the surface of the black hole—this point of distance to the black hole is known as the event horizon. 

A diagram of the regions of a black hole in space-time.

      What matter gets sucked into is known as the singularity of a black hole. The center of a black hole, the singularity, is the point where matter is compressed into infinite density. The gravitational pull is infinite, and space-time ceases to exist meaningfully. All nebulae, planets, asteroids and stars that get pulled into the center of a black hole are crushed and exist in some timeless, spaceless, inescapable space purgatory.
      Or do they? Beyond the event horizon of a black hole, scientists don’t really know for sure what happens inside of a black hole. Any foray into a black hole would never make it back to Earth, and the pull black holes have on light make it impossible for telescopes to study a black hole directly; scientists deduce the existence of black holes mainly through examining the orbits of objects in space around it. Because of this inability to study black holes more closely, black holes remain very mysterious.
      Luckily for humankind, no black holes exist even close to Earth. It begins to feel a little luckier, sitting on the edge of the Milky Way galaxy, far away from the mysterious, roiling center where Sagittarius A* looms. But just considering their properties— a gravitational force that dominates even the speed of light, the spectacular origins of stellar black holes, and the curious centrality every supermassive black hole holds in each galaxy— it's no wonder black holes capture the attention of scientists, authors, and the everyday student so easily. One might say that the study of black holes has at least metaphorically sucked in humankind.

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Curious about black holes? Come join the Marin Science Seminar for Dr. Eliot Quataert's presentation, 'Black Holes: The Science Behind Science Fiction,' tomorrow on Wednesday, March 13th. The Marin Science Seminar is located at Terra Linda High School, in room 207, from 7:30 to 8:30 p.m. Check us out on Facebook!

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Sandra Ning

Sunday, March 10, 2013

Check out the Marin Science Seminar Vimeo Channel

Check out Marin Science Seminar's Vimeo channel!

Here's MSS intern Josh Leung teaser video for this month's Astronomy speaker series.



Astronomy and Astrophysics - March 2013 from Marin Science Seminar on Vimeo.
March 6th: NASA's Fermi Gamma-ray Space Telescope (formerly known as GLAST) mission was launched into orbit on June 11, 2008. Its mission is to explore the most energetic and exotic objects in the cosmos: blazing galaxies, intense stellar explosions and super-massive black holes. Using experimental technologies developed by high energy particle physicists, Fermi's astrophysical observations are being conducted by scientists world-wide. Unlike visible light, gamma rays detected by Fermi's Large Area Telescope are so energetic that E = mc2 really matters! I will explain how Fermi uses matter and anti-matter pair production to track gamma rays to their cosmic locations, and will showcase recent exciting results from the mission

March 13: "I will begin by describing what black holes are (and what they are not!). I will then discuss how big black holes at the centers of galaxies are discovered, how they form, and how they give rise to some of the most remarkable and bizarre phenomena in the universe."

March 27: One of the fundamental goals of astronomy and astrophysics is to understand how the Universe and its constituent galaxies, stars, and planets formed, how they evolved, and what their destiny will be. Dr. Barsony's research is focussed on the formation of stars, brown dwarfs, free-floating planets, and planetary systems. The raw material is provided by the tenuous interstellar gas found in frigid clouds in our Galaxy. Since the present birthplaces of stars are hidden by interstellar dust mixed in with the gas, exploring the detailed mechanisms involved in star (and planetary system) formation requires observations at wavelengths whose passage is relatively unimpeded by the intervening dust: radio, millimeter, submillimeter, infrared, and X-ray wavelengths.

Monday, March 4, 2013

Fermi's Eye on the Universe

by Sandra Ning, Terra Linda HS

An image of the Milky Way Galaxy and its surroundings, by Fermi.

    Since their invention, telescopes have allowed humans to examine closely, and in more detail, the universe around them. Advances in optic technology have brought humans closer to understanding the microscopic world around us and the far-away mysteries above us. Telescopes like Hubble and Chandra directed into space have been sending back dazzling pictures of nebulae, galaxies and star clusters that are as beautiful as they are scientifically fascinating. Fermi joins the research team with new equipment: gamma- ray sensing technology.
    Dr. Lynn Cominsky, who is the Department Chair of Physics and Astronomy at Sonoma State University, stopped to answer a couple of questions about her upcoming presentation on NASA's Fermi Gamma-ray Space Telescope. She also lent her expertise to explaining the various, fascinating phenomena that occur out in the vast expanse of space.

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1. What is the goal of the Fermi Gamma-ray Telescope mission?

From http://fermi.gsfc.nasa.gov/science/

Mission Objectives:
  • Explore the most extreme environments in the Universe, where nature harnesses energies far beyond anything possible on Earth.
  • Search for signs of new laws of physics and what composes the mysterious Dark Matter.
  • Explain how black holes accelerate immense jets of material to nearly light speed.
  • Help crack the mysteries of the stupendously powerful explosions known as gamma-ray bursts.
  • Answer long-standing questions across a broad range of topics, including solar flares, pulsars and the origin of cosmic rays.
2. What sorts of cosmic substances/structures is Fermi looking for?

     Most of the objects that Fermi sees are Active Galaxies which are aiming jets of gamma rays towards Earth (also known as blazars).
     Fermi is also discovering many pulsars, gamma-ray bursts, solar flares, supernova remnants and a handful of other objects, such as high-mass binaries, novae and extended objects like the "Fermi bubbles."


Gamma-ray emissions around the Milky Way, detected by Fermi.

3. How are black holes formed? Why are supermassive ones, like Sagittarius A*, often (always?) at the center of galaxies?

     We don't know exactly how the supermassive black holes are formed. Current research indicates a correlation in size between the size of the galactic bulge and its black hole's mass. This would indicate that both the BH and the galaxy were formed together, when structure
began to form about a 500 million years after the Big Bang. Supermassive BHs are always at the centers of galaxies, as they are the most massive objects in the galaxy.

4. What about white holes and wormholes? Are they purely theoretical, 

     White holes and wormholes are theoretically allowed by Einstein's theory of General Relativity. However, we know of no earthly-substance that could go into a BH and come out a WH without being destroyed.
or even fictional?

     White holes and wormholes are theoretically allowed by Einstein's theory of General Relativity. However, we know of no earthly-substance that could go into a BH and come out a WH without being destroyed.

5. What are pulsars?

     Pulsars are rotating cores of dead stars - about the size of a large city. They are formed when regular, massive stars end their lives in supernova explosion. The outer layers of the star are ejected out, while the inner layers collapse down to form the pulsar. They also have very strong magnetic fields, which channel the particles and gamma-rays  in opposite directions.

6. And why are all of these high-energy phenomena of interest to researchers? How much (or perhaps, how little) do we know about these cosmic events that Fermi is looking for?

     Researchers are excited to study the most exotic and energetic phenomena in the Universe - we cannot duplicate the extreme conditions on Earth that naturally occur in space. Extreme magnetic fields, strong field gravity, high temperatures - all are of interest to scientists, as we can test our laws of physics at these extremes.


The Fermi satellite.


7. How does gamma-ray detection help Fermi in its mission? Is Fermi the only telescope with gamma-ray detection at the moment?

     Fermi is a gamma-ray telescope. So it must detect gamma rays in order to accomplish its mission. AGILE is a smaller telescope that was built and launched by the Italians, a few months before Fermi.

8. Aren't gamma rays without mass? How exactly does Fermi detect gamma rays?

     Gamma rays are the highest-energy form of light, and all forms of light are massless. Fermi has two instruments: the Large Area Telescope and the Gamma-ray Burst Monitor. Each detects the gamma ray light in a different manner.

You can read about the LAT here:
http://fermi.gsfc.nasa.gov/science/instruments/lat.html

You can read about the GBM here:
http://fermi.gsfc.nasa.gov/science/instruments/gbm.html

9. As part of the public outreach program for Fermi, why do you believe its important for the public to know about projects
like Fermi?

     Everyone is curious about the Universe - where we came from, where we are going, and are we alone? Fermi provides answers to some of these important questions. It is our job to explain Fermi's amazing discoveries to the public.

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Come see Dr. Cominsky present "Exploring the Extreme Universe with Fermi" on Wednesday, March 6th, in Terra Linda High School's room 207. This month is Astronomy Month for the Marin Science Seminar. Check out our Facebook for more updates!

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Sandra Ning