Sunday, June 26, 2011

solar sinter project

you can make glass by melting sand. here is a video showing markus kayser's fascinating machine that uses energy from the sun to create 3D structures of glass from sand in the sahara desert!

"Solar-sintering aims to raise questions about the future of manufacturing and triggers dreams of the full utilisation of the production potential of the world’s most efficient energy resource - the sun. Whilst not providing definitive answers, this experiment aims to provide a point of departure for fresh thinking."

Markus Kayser - Solar Sinter Project from Markus Kayser on Vimeo.

Friday, June 24, 2011

Supernovae Conference Day 3

the results presented at day 3 of the supernovae and their host galaxies were largely based on the highly productive Palomar Transient Factory (PTF), which is "a fully-automated, wide-field survey aimed at a systematic exploration of the optical transient sky." transients are objects that appear and disappear and can range from supernovae to asteroids to gamma ray bursts to comets, etc...

things i learned from today's speakers:

  • about 6000 supernovae have been identified ever by humans.
  • newly decorated PhD Mansi Kasliwal stated that the palomar transit factory (PTF) has identified 1178 extragalactic transits!
  • the PTF looks primarily for supernovae, but finds 50,000 asteroids every night!!
  • over the last few years, about 300 supernovae per year have been found (as reported by the International Astronomical Union).   the bad astronomer, phil plait, responded to my tweet of this fact to add some perspective:  "To give you an idea of how much better we are at finding SNe now: in 1987, the first one seen was in late February."
  • PTF has found 15 supernovae with very faint, very far (~100 kpc), or non-existent galaxy hosts!?! mysterious!
  • Robert Quimby talked about some (unexpectedly) extremely bright supernovae he has discovered.   many people at the conference are referring to this new class of super-luminous supernovae as "the quimbies" which i think is a great name! 

one example of these objects is supernova 2006gy, which reached 10x brighter than a typical type Ia SN and lasted for 5 months!  and for some strange reason, the quimbies seem to prefer dwarf galaxy environments.   below are 4 examples of quimbies as seen by the PTF.  the left images show the regions before, and the right show the regions just after the supernova explosions!

PTF09atu, PTF09cnd, PTF09cwl, and PTFcwr. Credit: Robert Quimby/Caltech/Nature

to read about more about these exotic supernovae, astronomy now has a nice interview with quimby that you can read/listen to here.

intro to the conference: here
summary of day 1: here
summary of day 2: here

Thursday, June 23, 2011

Supernovae Conference Day 2

some points of interest from day 2 of the supernovae and their host galaxies conference being held here in sydney this week....

Alicia Soderberg talked about the necessity to observe supernovae at radio wavelengths, in addition to the traditional optical spectral follow-up. radio observations give insight to the elusive progenitor stars and environments in which stars explode. radio emission from supernovae explosions originates from the interaction of the explosive shock wave with surrounding materials. a high radio flux indicates either the presence of dense interstellar material, or material present or stellar winds from a nearby "donor star."

she also acknowledged that "what made the Very Large Array (VLA) move" to the Whirlpool Galaxy (M51) a little less than a month ago, was the announcement by amateur astronomers on Twitter, that a star exploded in the nearby galaxy!

according to alex filippenko, professor of astronomy at the university of california, berkeley, and supernova expert who happened to be at the twin 10-meter Keck telescopes at the time of the twitter announcement,

"This is the first time that we've been alerted via a tweet. We've been alerted many times via email, and in a sense, I was alerted via an email message, but it was from a colleague who was alerted through a tweet. To my knowledge, that is unprecedented."

the very fist picture taken of the SN2011dh is shown below, even though it was not the source of the original announcement. these were taken by Manolo Barco, an amateur astronomer cordoba, spain.

Avishay Gal-Yam finally gave an explanation of the physical descriptions behind the different core-collapse supernova types (i couldnt remember the distinctions from my grad school classes...). Type II supernovae are believed to result from stars that have a helium and a hydrogen shell of surrounding gas before they explode.

there is also a trend such that as you go to the right in the diagram above, you tend to find those supernovae in galaxies with higher metallicity. Both Gal-Yam and Maryam Modjaz were careful to point out that the metallicity should be measured from the region around the supernovae explosion and not estimated over the full galaxy.

one topic that really interested me was the destruction and production of dust caused by supernova explosions. any dust present in the near vicinity of the star is vaporized by the initial explosion, but then more is formed over time on the molecules formed by the outward moving shock wave. the destruction is also dependent on dust grain size, such that small grains are more easily destroyed in the detonation and therefore large grains (>0.01 microns) survive.

estimations from very distant quasars reveal they should harbour 10^8 solar masses of dust already when the universe was less than a billion years old. in order for that much dust to be present, each supernova needed to produce between 0.1 and 1 solar mass of dust. observations, unfortunately, are not very good yet at constraining these values. based on the line profiles of optical spectra and thermal infrared excess, observations have given values of 0.0001 and 2 solar masses of dust present in supernova remnants!?! tough measurements to make and models to produce. will the herschel space telescope reveal more? time will tell.

UPDATE: summary of Day 1

Monday, June 20, 2011

Supernovae Conference Day 1

its interesting to attend a conference so specialized in a area that is not my exact area of expertise. i'm learning a lot, but i'm also tuning out a lot of details that dont fit into any "big picture" scenario that makes sense to me, even if its very relevant to the field of study of supernovae.

one interesting thing about studying transient phenomena is that you never know when they will appear and they fade over time. sometimes you apply for time at telescopes not knowing whether you will actually find anything to look at! in order to catch stars exploding, many groups of people survey over and over specific galaxies that are likely to have a supernova explosion. amateur astronomers have made a huge contribution over the years looking at the same galaxies many times and identifying changes that they see by eye!

stuart ryder focused on several candidate galaxies twice a year for 2.5 years with the gemini telescope and its adaptive optics and found 6 dusty stellar explosions!

one thing i appreciate more now is that there are A LOT of different types of supernova. Weidong Li showed that the overall split is such that about 75% of them originate from the core collapse of single massive stars and ~25% are from explosions caused by extra material falling onto white dwarf stars (see brief review: here). he also suggested that smaller galaxies tend to have higher supernova rates, but i wasnt entirely convinced of that result.

one interesting result was looking at the progenitors of supernova. its impossible to predict exactly when a star might explode, especially considering there are thousands of millions of stars in each galaxy, stars are not usually individually resolved, and most are too faint to ever detect before they go supernova. but, stephen smartt showed 5 instances where looking back at hubble space telescope images of nearby galaxies where supernovae have exploded has allowed the identification of a star before the explosion, and the lack of anything in the star's previous position after the supernovae fade.

in the images below, the white circles identify the star before (a), during the supernova (b), and after (c) the explosion. the images arent exactly the super pretty hubble images you might be used to, but they show that these stars really do explode!!

neat stuff. hope to post more tomorrow...

intro to the conference: here
summary of day 1: here
summary of day 2: here
summary of day 3: here

Sunday, June 19, 2011

Supernovae and their Host Galaxies

this coming week, sydney is hosting a professional astronomical conference called "Supernovae and their Host Galaxies," sponsored by the Australian Astronomical Observatory and CSIRO Astronomy and Space Science (i can never remember what CSIRO stands for...).

while supernovae (exploding stars) are not my research area of expertise, i signed up to attend the conference because, well, who doesnt like a good extragalactic stellar explosion?!? no seriously, i study the galaxies that these evolved stars live in and there are so many international experts in the field attending that i thought it would be an excellent way to catch up with the best current ideas as to how and why these stars explode.

Tycho's Supernova Remnant.  Credit: NASA/CXC/Rutgers/ J.Warren & J.Hughes et al.

i'll explain the basics of my knowledge of supernovae here (supernovae or supernovas are the plural forms of supernova) and throughout the week, i'll try to expand and update the current understanding based on what i find interesting at the conference. i'll also be using twitter to mention things in real time so follow there as well if you wish.

first, the lovely conference poster:

there are two fundamental ways stars explode as supernovae: from the central collapse of a single massive star, or from a thermonuclear detonation caused by too much extra material falling onto an old star. astronomers descriptively call these various explosions Type Ia, Type Ib, Type Ic, Type II, etc... based on the chemical signatures seen in their spectra when they were first being discovered and observed with telescopes.

1) Core-Collapse Supernovae are the inevitable explosions of big stars that are between 9 and ~40 times the mass of our sun (note that our sun will not go supernova because it is not massive enough). these massive stars burn big and bright during their lifetimes because deep in their central cores, they are fusing smaller elements into heavier ones through nuclear fusion. just as a campfire will burn out if you stop adding wooden logs for fuel, the centers of stars eventually run out of fuel for nuclear fusion. once this happens the core collapses in less than a second due to gravity and forms an extremely dense beast called a neutron star!

the heat and energy produced by the formation of the neutron star reverses the gravitational implosion and causes all the other material to shoot out in all directions at 50 million kilometers per hour! a powerful shock wave propagates outwards creating a visual outburst that can be as intense as the light of several billion suns. after reaching a maximum brightness, the supernovae fade slowly over a few months. these are classified as Type II, Type Ib and Type Ic supernovae and shown schematically below.

these supernovae are found mostly where there are lots of bright, young stars - in the arms of spiral galaxies. they are not found in elliptical galaxies which typically have old stars and very few young, newly-formed ones.

2) Thermonuclear Supernovae are called Type Ia and result from a completely different series of events. the process starts with an elderly star, called a white dwarf, which is what remains when a smallish ordinary star finishes its life cycle after running out of fuel for nuclear fusion in its core (our sun will eventually become a white dwarf star - in another 5 billion years or so).

white dwarf stars are typically very stable, but if a white dwarf star happens to have a nearby neighboring star that happens to shed enough gas onto white dwarf star that it reaches the so-called Chandrasekhar limit of 1.4 solar masses, the temperature in the core of the white dwarf will rise to the point of triggering explosive nuclear fusion reactions and releasing a huge amount of energy. the violent stellar explosion obliterates the star in about 10 seconds and releases an expanding cloud that glows brightly for a few weeks.

Type Ia supernovae are found in all types of galaxies.

so what mysteries remain? i'll leave you with the declared motivation for this conference from the organizers:

"The current generation of wide field transient surveys will revolutionize our understanding of why stars become supernovae. Designed to revisit large areas of sky at multiple wavelengths, these surveys are now discovering hundreds of supernovae each year. During the coming year, the number of supernova discoveries will increase even further as new transient surveys come online. As well as finding rare and possibly new types of supernovae, these surveys will generate new insights into both core-collapse and thermonuclear supernovae. It is therefore timely to have a conference that explores the current (observational and theoretical) supernova landscape and the connection between supernovae and their host galaxies."

intro to the conference: here
summary of day 1: here
summary of day 2: here
summary of day 3: here

Saturday, June 18, 2011

beyond escher

San Le is an artist and computer programmer who has taken ideas originated by MC escher to a different level. this week he posted a paper on the arXiv called "The Art of Space Filling in Penrose Tilings and Fractals." in this paper, he plays with the idea of tessellation, or tiling together of shapes in one plane. instead of using simple shapes like this example of penrose's aperiodic tiling using darts and kites:

Le applies images inside the kite and dart shapes like this:

the result is the creation of images that are at once mathematically stimulating and sensually interesting, like this:

Tuesday, June 14, 2011

x-ray rose

the work of nich veasey. i think the x-ray rose is nice.

the hands over the laptop though are a bit creepy!

Sunday, June 12, 2011

perception of science

its often that people ask me things like "what does a scientist actually do all day?" "how do you discover stuff?" "do you have to stay up all night?"

no, i dont usually stay up all night. i go to observatories with big telescopes every couple months for a week or two to collect data (optical data can only be collected at night, but radio observations can be taken 24 hours a day!), but mostly i'm sitting in front of my laptop (mac, in case you were wondering) working away at various tasks.

its hard to portray in movies the thrills of data reduction, statistical analysis, computer programming, or the time it takes to think through problems after inevitably getting stuck a few times.  so they dont.  instead, they show flashy lab equipment or the eureka! moments or scientists using computers to zoom into fuzzy images to miraculously increase the resolution! oh, if only the universe worked that way!

in reality, my day-to-day office work is completely different every day.  to give an idea, here is a list various things i've been working on over the last few weeks:

  • organizing recent research into a paper to submit to a journal
  • writing a talk for the Astronomical Society of Australia's Annual Scientific Meeting
  • finishing a proposal to use the parkes telescope early next year (ie. learning how radio astronomy works) 
  • learning to use python
  • finally getting my webpage up to date
  • responding to the comments a journal made on a research paper i recently submitted
  • helping to clean up a data set ("data reduction") taken at the AAO so that it's science-ready
  • organizing travel trips to advertise my research results and get feedback from experts around the world
  • trying to keep up to date with the literature and what other astronomers are doing
  • refereeing a journal paper submitted by another astronomer somewhere in the world
  • brainstorming about developing new instruments for old telescopes  and their potential science
  • helping organize professional workshops taking place in sydney
  • and probably other things that i cant remember right now.

usually i focus on one or two tasks to accomplish each day and priorities are set by hard deadlines. for instance, the telescope proposal is due early this week, so thats what i'm focusing on right now. but i also told my collaborators i'd finish the data reduction for them by the end of the week, so thats important. and i'd like to present some new results in my talk at the upcoming meeting so i have to test something i think i found in order to make sure it is a robust result and not caused by an observational bias of some sort.

and to be honest, i'm a bit spoiled right now because i do not have large time-consuming obligations to the observatory where i work, nor am i solely responsible for advising any PhD students, or teaching any classes.  so i'm in the lucky position of really being able to focus on research productivity, pursue new collaborative projects, and engage in public outreach (visiting schools, talking to amateur astronomy groups and teachers, public science writing, and writing songs about previous planets, etc..:).  

there are many different science questions i'm thinking about at any given time, with the goal of actually learning something towards their solutions that can be shared with humanity through discussion and publication.  each idea pops around the different stages of the "science in reality" section below with the hope that no research gets lost in the doldrums

so anyway, all of this was sparked by this "flowchart of the perception of science in popular culture versus actual science" i saw at electron cafe.   enjoy!

Thursday, June 9, 2011

twitter-based astronomy journal club

looking for a practical use for twitter? introducing the astronomy twitter journal club! a paper has been chosen, so read up and participate in the discussion via twitter (#astroJC) next thursday, june 16th at 8pm UT.

(the only impractical aspect for me is that the discussion will take place at 5am sydney time [check your local time here]. oh well... the good thing about twitter is that i can catch up with the discussion when i finally wake up!)

the paper: Gamma Rays From The Galactic Center and the WMAP Haze by Hooper & Linden, 2010

Abstract: Recently, an analysis of data from the Fermi Gamma Ray Space Telescope has revealed a flux of gamma rays concentrated around the inner ~0.5 degrees of the Milky Way, with a spectrum that is sharply peaked at 2-4 GeV. If interpreted as the products of annihilating dark matter, this signal implies that the dark matter consists of particles with a mass between 7.3 and 9.2 GeV annihilating primarily to charged leptons. This mass range is very similar to that required to accommodate the signals reported by CoGeNT and DAMA/LIBRA. In addition to gamma rays, the dark matter is predicted to produce energetic electrons and positrons in the Inner Galaxy, which emit synchrotron photons as a result of their interaction with the galactic magnetic field. In this letter, we calculate the flux and spectrum of this synchrotron emission assuming that the gamma rays from the Galactic Center originate from dark matter, and compare the results to measurements from the WMAP satellite. We find that a sizable flux of hard synchrotron emission is predicted in this scenario, and that this can easily account for the observed intensity, spectrum, and morphology of the "WMAP Haze".

follow along at hashtag: #astroJC
brought to you by @astronomyjc

Wednesday, June 8, 2011

puyehue volcano eruption

after silence for 50 years, the puyehue volcano in southern chile erupted on saturday. there are many amazing photos here, but i think these two are stunning:

Tuesday, June 7, 2011

what an astronaut's camera sees

NASA's Dr. Justin Wilkinson narrates this video which shows gorgeous views of various places on earth, captured digitally by the astronauts while floating in orbit.

Saturday, June 4, 2011


miles pasick claims he was inspired by this passage from john milton's paradise lost when creating the painting below:

"For who would lose,
Though full of pain this intellectual being,
Those thoughts that wander through eternity,
To perish rather, swallow’d up and lost,
In the wide womb of uncreated night?"
-Paradise Lost. Book ii. Line 146.

Wednesday, June 1, 2011

timelapse: australia telescope compact array

the australian telescope compact array in northern NSW, australia, is a collection of six 22-meter antennas used for radio astronomy. i'm currently working on a proposal for a project that would allow me to use them in about 6 months - if the "time allocation committee" decides my idea is good compared to all the other proposals that get submitted.

this timelapse video of the facility is lovely, but i'm drawn to the shots of birds and wildlife for some reason :)