Tag Archives: stars

#WomeninSTEM: Book “The Glass Universe”

Today, 11th February, we’re celebrating the International Day of Women and Girls in Science. Introduced by the UN in December 2015, this is the second year it is done. This International Day recognizes the critical role women and girls play in science and technology communities, and aims to promote events that support and promote the access of women and girls and their participation in science, technology, engineering and mathematics education, training and research activities at all levels.

For this I really recommend the wonderful new book by famous science writer Dava Sobel: The Glass Universe. This book describes the challenges and achievements at Harvard College Observatory (U.S.A.), when in the mid-nineteenth century began employing women as calculators, or “human computers”, to interpret the observations their male counterparts made via telescope each night. Observations were taken with the new technique of photography.

In particular, they used glass photographic plates (in few decades they got almost half a million of them!) and, as “readers of books written in glass”, these women made extraordinary discoveries that definitively changed the way we understood the stars and the Universe. They helped discern what the stars were made of, divided them into meaningful categories for further research, and even found a way to measure distances across space by starlight. The lifes and works of all these women are truly inspiring.

Book "The Glass Universe" by Dava Sobel. Wonderful.

Book “The Glass Universe” by Dava Sobel. Wonderful.

I’m still half way through the book, but I’ll update this post during the week providing extra information about what I’ve found most fascinating on it. Believe me I’m finding many discoveries reading  “The Glass Universe“, starting with realizing how “reading the lines of the stars” (spectroscopy) was done in those times.

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Video of the “Story of Light” in Vivid Sydney 2016

Following the success of our sold-out Event “The Story of Light – The Astronomer’s Perspective” for ViVID Sydney Ideas 2015, the Australian Astronomical Observatory (AAO) continued its collaboration with ViVID Sydney 2016 organizing “The Story of Light – Deciphering the data encoded on the cosmic light”. But actually it was me who was in charge of the organization.

The five astronomers speaking during our “Sydney Vivid Ideas: The Story of Light” started at the Powerhouse Museum, Sydney, 29th May 2016. From left to right: Luke Barnes, Alan Duffy, Vanessa Moss, Liz Mannering and Ángel López-Sánchez. Photo credit: Jenny Ghabache (AAO).

The event was held at the PowerHouse Museum in Sydney on Sunday 29th May 2016. More than 160 people attended this special event. Five young astronomers (me included) talked about Astronomy and Big Data: the light and light-based technologies developed in Australian astronomy for both optical and radio telescopes; the tools, platforms, and techniques used for data analysis and visualization; how astronomers create simulation data; how some of these techniques are being used in other research areas; and the major scientific contributions toward our understanding of the Universe. Indeed, astronomers have been pioneers in developing “Data Science” techniques to make sense of this huge data deluge, many of which are now used in other areas.

We recorded all the event in video, and it is now publicly available  in the AAO YouTube channel. Some photos of the event are also compiled below. I want to thank AAO/ITSO Research Astronomer Caroline Foster for helping recording and editing the video and Jenny Ghabache (AAO) for taking the photos of the event.

Full recording of the event “The Story of Light 2016: Deciphering the data encoded on the cosmic light” organised by the AAO for Vivid Sydney Ideas 2016. Credit: AAO. Acknowledgment: Caroline Foster (AAO).

The event was hosted by Alan Duffy (Swinburne University). I was in charge of explaining optical astronomy, the AAO, optical surveys and big data. Then my colleagues  Vanessa Moss (Univ of Sydney/CAASTRO), Luke Barnes (Univ. of Sydney) and Liz Mannering (AAO/ICRAR) discussed radio astronomy, the ASKAP and big data (Vanessa), simulating, analysing and visualizing astronomy data (Luke) and astronomy data archive, the All-Sky Virtual Observatory (ASVO) and other virtual observatories (Liz ). After the short 12-15 minutes talks (well, as usual I took a bit more time), the panel welcomed questions from the audience (and even from Twitter using #SoLSydneyIdeas) for a discussion session about Light and Astronomy and the Australian contribution to the improvement of our understanding of the Universe.

The Lecture Theatre a few minutes before our “Sydney Vivid Ideas: The Story of Light” started at the Powerhouse Museum, Sydney, 29th May 2016. Photo credit: Jenny Ghabache (AAO).

Our host, Alan Duffy, introducing the event. Photo credit: Jenny Ghabache (AAO).

AAO/MQU Research Astronomer Ángel R. López-Sánchez talking about optical astronomy, the AAO and big data. Photo credit: Jenny Ghabache (AAO).

Vanessa Moss (Univ. of Sydney/CAASTRO) talking about radioastronomy, the ASKAP and big data. Photo credit: Jenny Ghabache (AAO).

Luke Barnes (Univ. of Sydney) talking about simulating, analysing and visualizing astronomy data. Photo credit: Jenny Ghabache (AAO).

Liz Mannering (Univ. of Sydney) discussed astronomy data archive, the All-Sky Virtual Observatory (ASVO) and other virtual observatories. Photo credit: Jenny Ghabache (AAO).

Panel discussion with all participants answering questions from the audience. Photo credit: Jenny Ghabache (AAO).

Angel Lopez-Sanchez answering a question from the audience. Photo credit: Jenny Ghabache (AAO).

And last… Well, if you want to see only my talk, here it is:

A year since the “Multiwavelength Dissection of Galaxies” Conference

I cannot believe a FULL YEAR has already gone since the “Multiwavelength Dissection of Galaxies” Conference happened. And I have never found the time to just describe how much work this was for me, and at the success of this meeting. At least let me share today the article I wrote for “The Observer”, the AAO Newsletter.

 
The Southern Cross Astrophysics Conferences, which are jointly supported by the Australian Astronomical Observatory (AAO) and the CSIRO Astronomy and Space Science (CASS), are held annually around Australia with the aim of attracting international experts with wide ranging skills to discuss a particular astrophysical topic. The conference “Multiwavelength dissection of galaxies”, which was held at the Crown Plaza Hotel in  Coogee Beach, Sydney between 24th – 29th May 2015, was the 8th of the Southern Cross Conference Series. This Conference focused on galaxy evolution, combining resolved optical/near-infrared integral field spectroscopy data with other multiwavelength properties (from X-ray to radio) of nearby galaxies plus giving the view of what is known in our Milky Way.

Poster of the Conference "Multiwavelength Dissection of Galaxies".

Poster of the Conference “Multiwavelength Dissection of Galaxies”.

Indeed, the number of studies of galaxies using integral field spectroscopy (IFS) is rapidly increasing as a consequence of surveys such as ATLAS-3D, CALIFA, SAMI (that is conducted at the AAT), or MANGA. IFS techniques allow to spatially resolve internal properties of galaxies with unprecedented detail, and therefore they are providing key clues for understanding the structural components of galaxies, their star-formation activity, kinematics, stellar populations, metal distribution, and nuclear activity, as well as how galaxies evolve with time. Nevertheless, for a complete picture of how galaxies work it is crucial to use other multi-wavelength results, targeting galaxies in X-ray, ultraviolet, infrared, and radio frequencies. In particular, HI radio-surveys such as HIPASS, LVHIS, THINGS, Little-THINGS, ALFALFA, HALOGAS or WALLABY are essential to trace the neutral gas content of galaxies, as the 21 cm HI radio data provide key information about how the cold gas in converted into stars and galaxy dynamics. At the same time we are notably increasing our knowledge of the structure and composition of the Milky Way. This is possible thanks to the combination of very detailed observations of individual stars (such those coming from the RAVE survey conducted at the 1.2m UKST or the on-going GALAH survey at the AAT using the new high-resolution HERMES spectrograph), detailed analyses of Galactic nebulae, large field studies of the interstellar medium, and surveys searching for the diffuse gas with and around our Galaxy.

Hence, the aim of the “Multiwavelength dissection of galaxies” Conference was to bring together international experts in both Galactic and extragalactic astronomy to discuss the different components of a galaxy: stars, gas, dust, and dark matter, and where these components are found within and around galaxies, from both an observational (from radio to X-rays, but with a fundamental optical IFS component) and a theoretical point of view (from the most recent simulations of galaxy assembly to models reproducing the chemical evolution of galaxies), with the final objective of getting a better understanding on the processes that rule the evolution of the galaxies.

Conference Photo with the majority of the participants to the “Multiwavelength Dissection of Galaxies” meeting, 24th - 29th  May 2015. The background is an image of the Southern sky showing the Southern Cross and the Pointers. Credit: Conference Photo: Andy Green (AAO), Background image & composition: Ángel R. López-Sánchez.

Conference Photo with the majority of the participants to the “Multiwavelength Dissection of Galaxies” meeting, 24th – 29th May 2015. The background is an image of the Southern sky showing the Southern Cross and the Pointers. Credit: Conference Photo: Andy Green (AAO), Background image & composition: Ángel R. López-Sánchez.

Around 120 astronomers all around the globe attended to this Conference. In five days we had 94 talks, including 27 invited talks and a Summary talk, and 26 poster contributions. Highlight invited talks were given by Rosemary Wyse (The Structure of the Milky Way), Naomi McClure-Griffiths (Neutral gas in and around the Milky Way), Baerbel Koribalski (Diffuse gas in and around galaxies), Christy Tremonti (Measuring Gas Accretion and Outflow Signatures with MaNGA), César Esteban (Ionized gas in the Milky Way), Evan Skillman (The Chemical Properties of the ISM of Nearby Galaxies), Sarah Martell (Introduction to the GALAH Survey), Geraint Lewis (Galactic Archeology in the Local Group), Alessandro Boselli (The dust emission properties of nearby galaxies after Herschel), Jakob Walcher (News about the interstellar medium in galaxies from the CALIFA survey), Stas Shabala (Resolving the mysteries of AGN feedback:radio jets, galaxies and citizen science), Joss Bland-Hawthorn (Near Field Cosmology), Martin Asplund (The Gaia-ESO survey), Richard Bower (The EAGLE Universe), Lisa Kewley (SAMI Science) and Molly Peeples (A Multiwavelength View of the Circumgalactic Medium).

We also organised a “Poster Contest”: participants were asked to vote for their 2 favourite posters, and they got a short (10 minutes) talk during the last session of the Conference. The winners were two PhD students: Christina Baldwin (Macquarie University, Australia, with the poster “Early-Type Galaxy Stellar Populations in the Near-Infrared”) and Manuel Emilio Moreno-Raya (Universidad Complutense Madrid and CIEMAT, Spain, with the poster “Dependence of SNe Ia absolute magnitudes on the host galaxies elemental gas-phase abundances”).

We have compiled all scientific presentations at the Conference Webpage:

http://www.aao.gov.au/conference/multiwavelength-dissection-of-galaxies

Furthermore, participants were very active in Twitter, that followed the hashtag of the Conference #MDGal15, allowing a wider diffusion of the main results speakers were presenting. We have also compiled all tweets in a Storify for each day, they are available in our website.

Besides the scientific talks, participants enjoyed the social events we organised for the Conference, including a Welcome Cocktail Cruise on Sunday 24th May (delegates enjoyed not only the great views of Sydney Harbour but also a starry sky and the famous ViVID Lights Sydney Festival), a Wine Tasting event on Tuesday 26th, an outdoors barbecue and a visit to Sydney Observatory and Stargazing on Wednesday 27th May, and the Conference Dinner on Thursday 28th May, which was held at the Spanish restaurant “Postales” in famous Martin Place, Sydney. Furthermore, the AAO organised the Public Event “The Story of Light: The Astronomer’s Perspective” on Sunday 24th May at the Powerhouse Museum (Sydney). This event, which was fully booked, was included as part of the ViVID Festival and connected the International Year of Light 2015 with our Conference.

Overall, we considered it was a great Conference and some important and controversial research topics were actually discussed during those five days, generating new ideas and projects, and many new collaborations between participants (even between Galactic and extragalactic astronomers) started there.

Finally, I would like to thank the impeccable organisation of the staff at Crown Plaza Hotel, as everything worked very smoothly and we didn’t have any problems at all during our Conference. In particular, coffee breaks and lunches were very well attended, and we really enjoyed a great quality food. Of course, I also must thank all the members of the LOC and the SOC committees for their invaluable help organising this Conference. In particular, I would like to thank Helen Woods (AAO) for her enormous effort and Andrew Hopkins and AAO’s Director, Warrick Couch, for their strong support to this meeting.

The oldest stars of the Galaxy

DP ENGLISH: This story belongs to the series “Double Post” which indicates posts that have been written both in English in The Lined Wolf and in Spanish in El Lobo Rayado.

DP ESPAÑOL: Esta historia entra en la categoría “Doble Post” donde indico artículos que han sido escritos tanto en español en El Lobo Rayado como en inglés en The Lined Wolf.

Last month the prestigious journal Nature published a letter led by PhD student (and friend) Louise Howes (@Lousie, ANU/RSAA, Australia). This scientific paper, with title Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way, uses data from the 1.2m Skymapper Telescope, the 3.9m Anglo-Australian Telescope (both at Siding Spring Observatory, NSW, Australia) and the 6.5m Magellan Clay telescope (Las Campanas Observatory, Chile) to study very old stars in the Milky Way bulge.

Image of the Galactic centre obtained using Skymapper data. Credit: Chris Owen (ANU/RSAA).

Image of the Galactic centre obtained using Skymapper data. Credit: Chris Owen (ANU/RSAA).

The aim of the research was to look for signatures of really old stars: stars that old that perhaps the Milky Was was not even born when they were created! How do astronomers know that? Just studying the chemical composition of the stars via deep spectral analysis. Only hydrogen and helium (and just a bit of litium) were formed in the Big Bang: the rest of elements have been created or inside the stars (oxygen, carbon, nitrogen, iron) or because of processes happening to the stars (e.g., supernova explosions, that create heavy elements such as gold, silver, copper or uranium). As time goes by and new generations of stars are born, the amount of metals (for astronomers, metals are all elements which are not hydrogen and helium) increases. Therefore if we discover a star with very few amount of metals, we will quite sure we are observing a very old object.

Loiuse has been using the 2dF instrument at the Anglo-Australian Telescope and the MIKE spectrograph at the Magellan Clay Telescope (Chile) to get deep, high-resolution spectra of candidate old stars in the Galactic bulge. The candidate stars were identified using optical images provided by the 1.2m Skymapper Telescope. With these observations, Louise Howes and collaborators have detected 23 stars that are extremely metal-poor. These stars have surprisingly low levels of carbon, iron and other heavy elements. Indeed, they report the discovery of a star that has an abundance of iron which is 10,000 times lower than that found in the Sun! These stars were formed at redshift greater than 15, that is, we are observing in our own Milky Way stars that were formed just ~300 million years after the Big Bang!

On top of that, the study suggests that these first stars didn’t explode as normal supernova but as hypernova: poorly understood explosions of probably rapidly rotating stars producing 10 times as much energy as normal supernovae. The high-resolution spectroscopic data have been also used to study the kinematics of these very old stars, that are found on tight orbits around the Galactic centre rather that being halo stars passing through the bulge. This is also characteristic of stars that were formed at redshifts greater than 15.

Short 3 minutes video discussing the results found in this study. Credit: ANU.

I’m happy to say here that I’ve been the support astronomer for many of her nights at the AAT the last couple of years. And I’m extremely happy to see that, even because of the bad weather we have had sometimes, they managed to get these observations published in Nature! Well done, Louise!

More details:

Scientific paper in Nature: Howes et al. 2015, Extremely metal-poor stars from the cosmic dawn in the bulge of the Milky Way, 11 November 2015.

Scientific paper in arXiv

ANU Press Release

Gas, star-formation and chemical enrichment in the spiral galaxy NGC 1512

How do galaxies grow and evolve? Galaxies are made of gas and stars, which interact in very complex ways: gas form stars, stars die and release chemical elements into the galaxy, some stars and gas can be lost from the galaxy, some gas and stars can be accreted from the intergalactic medium. The current accepted theory is that galaxies build their stellar component using their available gas while they increase their amount of chemical elements in the process. But how do they do this?

That is part of my current astrophysical research: how gas is processed inside galaxies? What is the chemical composition of the gas? How does star-formation happen in galaxies? How galaxies evolve? Today, 21st May 2015, the prestigious journal “Monthly Notices of the Royal Astronomical Society”, publishes my most recent scientific paper, that tries to provide some answers to these questions. This study has been performed with my friends and colleagues Tobias Westmeier (ICRAR), Baerbel Koribalski (CSIRO), and César Esteban (IAC, Spain). We present new, unique observations using the 2dF instrument at the 3.9m Anglo-Australian Telescope (AAT), in combination with radio data obtained with the Australian Telescope Compact Array (ATCA) radio-interferometer, to study how the gas in processed into stars and how much chemical enrichment has this gas experienced in a nearby galaxy, NGC 1512.

Deep images of the galaxy pair NGC 1512 and NGC 1510 using optical light (left) and ultraviolet light (right).Credit: Optical image: David Malin (AAO) using photographic plates obtained in 1975 using de 1.2m UK Schmidt Telescope (Siding Spring Observatory, Australia). UV image: GALEX satellite (NASA), image combining data in far-ultraviolet (blue) and near-ultraviolet (red) filters.

NGC 1512 and NGC 1510 is an interacting galaxy pair composed by a spiral galaxy (NGC 1512) and a Blue Compact Dwarf Galaxy (NGC 1510) located at 9.5 Mpc (=31 million light years). The system possesses hundreds of star-forming regions in the outer areas, as it was revealed using ultraviolet (UV) data provided by the GALEX satellite (NASA). Indeed, the UV-bright regions in the outskirts of NGC 1512 build an “eXtended UV disc” (XUV-disc), a feature that has been observed around the 15% of the nearby spiral galaxies. However these regions were firstly detected by famous astronomer David Malin (AAO) in 1975 (that is before I was born!) using photographic plates obtained with the 1.2m UK Schmidt Telescope (AAO), at Siding Spring Observatory (NSW, Australia).

The system has a lot of diffuse gas, as revealed by radio observations in the 21 cm HI line conducted at the Australian Telescope Compact Array (ATCA) as part of the “Local Volume HI Survey” (LVHIS) and presented by Koribalski & López-Sánchez (2009). The gas follows two long spiral structures up to more than 250 000 light years from the centre of NGC 1512. That is ~2.5 times the size of the Milky Way, but NGC 1512 is ~3 times smaller than our Galaxy! One of these structures has been somehow disrupted recently because of the interaction between NGC 1512 and NGC 1510, that it is estimated started around 400 million years ago.

Multiwavelength image of the NGC 1512 and NGC 1510 system combining optical and near-infrared data (light blue, yellow, orange), ultraviolet data from GALEX (dark blue), mid-infrared data from the Spitzer satellite (red) and radio data from the ATCA (green). The blue compact dwarf galaxy NGC 1510 is the bright point-like object located at the bottom right of the spiral galaxy NGC 1512.
Credit: Ángel R. López-Sánchez (AAO/MQ) & Baerbel Koribalski (CSIRO).

Our study presents new, deep spectroscopical observations of 136 genuine UV-bright knots in the NGC 1512/1510 system using the powerful multi-fibre instrument 2dF and the spectrograph AAOmega, installed at the 3.9m Anglo-Australian Telescope (AAT).

2dF/AAOmega is generally used by astronomers to observe simultaneously hundreds of individual stars in the Milky Way or hundreds of galaxies. Without considering observations in the Magellanic Clouds, it is the first time that 2dF/AAOmega is used to trace individual star-forming regions within the same galaxy, in some way forming a huge “Integral-Field Unit” (IFU) to observe all the important parts of the galaxy.

Two examples of the high-quality spectra obtained using the AAT. Top: spectrum of the BCDG NGC 1510. Bottom: spectrum of one of the brightest UV-bright regions in the system. The important emission lines are labelled.
Credit: Ángel R. López-Sánchez (AAO/MQ), Tobias Westmeier (ICRAR), César Esteban (IAC) & Baerbel Koribalski (CSIRO).


The AAT observations confirm that the majority of the UV-bright regions are star-forming regions. Some of the bright knots (those which are usually not coincident with the neutral gas) are actually background galaxies (i.e., objects much further than NGC 1512 and not physically related to it) showing strong star-formation activity. Observations also revealed a knot to be a very blue young star within our Galaxy.

Using the peak of the H-alpha emission, the AAT data allow to trace how the gas is moving in each of the observed UV-rich region (their “kinematics”), and compare with the movement of the diffuse gas as provided using the ATCA data. The two kinematics maps provide basically the same results, except for one region (black circle) that shows a very different behaviour. This object might be an independent, dwarf, low-luminosity galaxy (as seen from the H-alpha emission) that is in process of accretion into NGC 1512.

Map showing the velocity field of the galaxy pair NGC 1512 / NGC 1510 as determined using the H-alpha emission provided by the AAT data. This kinematic map is almost identical to that obtained from the neutras gas (HI) data using the ATCA, except for a particular region (noted by a black circle) that shows very different kinematics when comparing the maps.
Credit: Ángel R. López-Sánchez (AAO/MQ), Tobias Westmeier (ICRAR), César Esteban (IAC) & Baerbel Koribalski (CSIRO).

The H-alpha map shows how the gas is moving following the optical emission lines up to 250 000 light years from the centre of NGC 1512, that is 6.6 times the optical size of the galaxy. No other IFU map has been obtained before with such characteristics.

Using the emission lines detected in the optical spectra, which includes H I, [O II], [O III], [N II], [S II] lines (lines of hydrogen, oxygen, nitrogen and sulphur), we are able to trace the chemical composition -the “metallicity”, as in Astronomy all elements which are not hydrogen or helium as defined as “metals”- of the gas within this UV-bright regions. Only hydrogen and helium were created in the Big Bang. All the other elements have been formed inside the stars as a consequence of nuclear reactions or by the actions of the stars (e.g., supernovae). The new elements created by the stars are released into the interstellar medium of the galaxies when they die, and mix with the diffuse gas to form new stars, that now will have a richer chemical composition than the previous generation of stars. Hence, tracing the amount of metals (usually oxygen) within galaxies indicate how much the gas has been re-processed into stars.


Metallicity map of the NGC 1512 and NGC 1510 system, as given by the amount of oxygen in the star-forming regions (oxygen abundance, O/H). The colours indicate how much oxygen (blue: few, green: intermediate, red: many) each region has. Red diamonds indicate the central, metal rich regions of NGC 1512. Circles trace a long, undisturbed, metal-poor arm. Triangles and squares follow the other spiral arms, which is been broken and disturbed as a consequence of the interaction between NGC 1512 and NGC 1510 (blue star). The blue pentagon within the box in the bottom right corner represents the farthest region of the system, located at 250 000 light years from the centre.
Credit: Ángel R. López-Sánchez (AAO/MQ), Tobias Westmeier (ICRAR), César Esteban (IAC) & Baerbel Koribalski (CSIRO).


The “chemical composition map” or “metallicity map” of the system reveals that indeed the centre of NGC 1512 has a lot of metals (red diamonds in the figure), in a proportion similar to those found around the centre of our Milky Way galaxy. However the external areas show two different behaviours: regions located along one spiral arm (left in the map) have low amount of metals (blue circles), while regions located in other spiral arm (right) have a chemical composition which is intermediate between those found in the centre and in the other arm (green squares and green triangles). Furthermore, all regions along the extended “blue arm” show very similar metallicities, while the “green arm” also has some regions with low (blue) and high (orange and red) metallicities. The reason of this behaviour is that the gas along the “green arm” has been very recently enriched by star-formation activity, which was triggered by the interaction with the Blue Compact Dwarf galaxy NGC 1510 (blue star in the map).

When combining the available ultraviolet and radio data with the new AAT optical data it is possible to estimate the amount of chemical enrichment that the system has experienced. This analysis allows to conclude that the diffuse gas located in the external regions of NGC 1512 was already chemically rich before the interaction with NGC 1510 started about 400 million years ago. That is, the diffuse gas that NGC 1512 possesses in its outer regions is not pristine (formed in the Big Bang) but it has been already processed by previous generations of stars. The data suggest that the metals within the diffuse gas are not coming from the inner regions of the galaxy but very probably they have been accreted during the life of the galaxy either by absorbing low-mass, gas-rich galaxies or by accreting diffuse intergalactic gas that was previously enriched by metals lost by other galaxies.

In any case this result constrains our models of galaxy evolution. When used together, the analysis of the diffuse gas (as seen using radio telescopes) and the study of the metal distribution within galaxies (as given by optical telescopes) provide a very powerful tool to disentangle the nature and evolution of the galaxies we now observe in the Local Universe.

More information

Scientific Paper in MNRAS: “Ionized gas in the XUV disc of the NGC 1512/1510 system”. Á. R. López-Sánchez, T. Westmeier, C. Esteban, and B. S. Koribalski.“Ionized gas in the XUV disc of the NGC1512/1510 system”, 2015, MNRAS, 450, 3381. Published in Monthly Notices of the Royal Astronomical Society (MNRAS) through Oxford University Press.

AAO/CSIRO/ICRAR Press Release (AAO): Galaxy’s snacking habits revealed

AAO/CSIRO/ICRAR Press Release (ICRAR): Galaxy’s snacking habits revealed

Royal Astronomical Society (RAS) Press Release: Galaxy’s snacking habits revealed

Article in Phys.org: Galaxy’s snacking habits revealed

Article in EurekAlert!: Galaxy’s snacking habits revealed

Article in Press-News.org: Galaxy’s snacking habits revealed

Article in Open Science World: Galaxy’s snacking habits revealed

ATNF Daily Astronomy Picture on 21st May 2015.

Timelapse video: The Sky over the Anglo-Australian Telescope

A dark winter night, with the Milky Way crossing the firmament while its center in located near the zenith, is one of the most astonishing views we can enjoy. This vision is only obtained from the Southern Hemisphere and it is really inspiring. In particular, the Milky Way shines over the Siding Spring Observatory, near Coonabarabran (NSW), where the famous Anglo-Australian Telescope (AAT) is located. With the idea of sharing the beauty of the night sky to everybody, in May 2011 I decided to start taking timelapse photography while I was working as support astronomer at the AAT. This technique consists on taking many images and then adding all to get a movie with a very high resolution. The best shots I obtained by September 2011 were included in the video The Sky over the Anglo-Australian Telescope, which is available both in YouTube and in several MOV/MP4 files (HD, iPad, iPhone) in my personal AAO webpage.


“The Sky over the Anglo-Australian Telescope” was my first public timelapse video, released in November 2011.
Credit: Ángel R. López-Sánchez (AAO/MQ), the credit of the music is Echoes from the past, by Dj Fab.

The video, which lasts for 2.7 minutes, is the results of combining around 3800 different frames obtained using a CANON EOS 600D between June and September 2011. Except for those frames used for the sunset in the first scene, all frames have a 30 seconds exposure time, with a ISO speed of 1600. As the videos were created at 24 fps (frames per second), each second in the movie corresponds to 12 minutes in real time. I used several lens to take the images (standard 50 mm, 50mm x 0.65 focal reducer and a 10 mm wide-angle lens). The focal chosen was 5.6 (for the 50 mm lens) or 4.5 (10 mm wide-angle lens). Processing each sequence of the movie took five to six hours of computer time, and usually I had to repeat this at least once for each sequence, to improve the quality. The soundtrack I chose is an extract of the music Echoes from the past, by the french composer Dj Fab, which gives energy to the timelapse.

The Milky Way is setting at Siding Spring Observatory on 21 Sep 2011.
Click here to get the full resolution frame.
Credit: Á.R. L-S.

As my main job while I’m at the AAT is providing instrumental and scientific support to the astronomers who are observing in this telescope, I always set the camera up at the beginning of the night, let it run, and check on its progress occasionally. Sometimes this was not easy: wind knocked the camera over on a couple of times, often the battery ran out, and even once I had an encounter with some intransigent kangaroos. However, finally I got this material, which does not only show the magnificent Milky Way rising and setting above the dome of the AAT, but also stars circling the South Celestial Pole, the Magellanic Clouds over the AAT, satellites and airplanes crossing the sky, the Moon rising and setting, and the most famous constellations as Orion, Carina and the Southern Cross.

Circumpolar star traces (2.7 hours) over the Anglo-Australian Telescope on 20 Sep 2011.
Click here to get the full resolution frame.
Credit: Á.R. L-S.

I hope you enjoy the result. More timelapse videos to come soon!

The importance of massive stars

The mass range of stars drawing their energy supply from nuclear fusion covers about three orders of magnitude. The least massive stars known have masses around 0.1 solar masses (M) and the most massive examples are around 100 M, although stars with masses of ~150M may also exist.

Massive stars are defined as those stars with masses higher than around 8 M. However, this lower limit is not completely fixed, as the definition of massive star actually comes from those stars that ignite helium and afterwards carbon in non-degenerated stellar cores (i.e., the hydrostatic equilibrium is reached because the inward gravitational force is balanced with the outward force due to the pressure gradient of the gas). Depending on the evolutionary scenario, this happens between 7 and 9 M.

Massive stars consume their fuel faster than low and intermediate mass stars: a solar-mass star has a life ~125 times longer than a 10 M star. Massive stars also are very luminous: a 100M star shines with a luminosity similar to ~1600 Suns. Hence, except for stars of transient brightness, like novae and supernovae, hot, massive stars are the most luminous stellar objects in the Universe.

Young, massive star clusters near the center of the Milky Way, at ~25,000 light-years from Earth: the Arches cluster (left) and the Quintuplet Cluster (right). Both pictures were taken using infrared filters by the NICMOS camera of the Hubble Space Telescope in September 1997. The galactic center stars are white, the red stars are enshrouded in dust or behind dust, and the blue stars are foreground stars between us and the Milky Way’s center. The clusters are hidden from direct view behind black dust clouds in the constellation Sagittarius. Credit: Don Figer (STScI) and NASA.

Massive stars are, however, extremely rare. Following the very famous results obtained by the Austrian-Australian-American astrophysicist Edwin Ernest Salpeter in 1955, the number of stars formed per unit mass interval is roughly proportional to M -2.35. Therefore we expect to find only very few massive stars in comparison with solar-type stars: for each 20M star in the Milky Way there are roughly a hundred thousand solar-type stars; for each 100M star there should be over a million solar-type stars.

However, despite their relative low number, massive stars have a fundamental influence over the interstellar medium and galactic evolution because they are the responsible of the ionization of the surrounding gas and they deposit mechanical energy first via strong stellar winds and later as supernovae, enriching the interstellar medium by returning unprocessed and nuclear processed material during their whole life. Massive stars therefore condition their environment and supply it with new material available for the birth of new generations of stars, being even the triggering mechanism of star formation. They also generate most of the ultraviolet ionization radiation in galaxies, and power the far-infrared luminosities through the heating of dust. The combined action of stellar winds and supernovae explosions in massive young stellar clusters leads to the formation of super-bubbles that may derive in galactic super-winds. Furthermore, massive stars are the progenitors of the most energetic phenomenon nowadays found, the gamma-ray bursts (GRBs), as they collapse as supernova explotions into black holes. Particularly, the interest in hot luminous stars has increased in the last decade because of the massive star formation at high redshift and the results of numerical simulations regarding the formation of the fi rsts stars at zero metallicity (Population III stars), that are thought to be very massive stars with masses around 100 100M.

The descents of the most massive, extremely hot (temperatures up to 200,000 K) and very luminous (105  to 106 solar luminosities, L) O stars are Wolf-Rayet stars, which have typical masses of 25 – 30 M for solar metallicity.