Category Archives: Spiral Galaxies

Image

Multiwavelength image of the spiral galaxy M 101

Multiwavelength image of nearby spiral galaxy M 101 combining ultraviolet (light blue), optical (green), near infrared (yellow), H-alpha and 8 microns mid-infrared (red) and 21 cm HI emission (dark blue). Each colour prepresents an important component of the galaxy: massive stars (light blue), stars (green and yellow), star-forming gas and dust (red) and neutral hydrogen (dark blue)

Compare with the Astronomical Picture of the Day on 13 July 2012 apod.nasa.gov/apod/ap120713.html

Data credit: UV data (GALEX): Gil de Paz et al. 2007, ApJS, 173, 185; R and Hα data (KPNO): Hoopes et al. 2001, ApJ, 559, 878; Near-Infrared data (2MASS): Jarrett et al. 2003, AJ, 125, 525, 8 microns data (Spitzer): Dale et al. 2009, ApJ, 703, 517; 21cm HI data (VLA): Walter et al. 2008, AJ, 136, 2563, ”The H I Nearby Galaxy Survey”.

Credit of the composition: Ángel R. López-Sánchez (AAO/MQ).

More sizes and high resolution image in My Flickr.

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Podcast in FBI radio: The Milky Way is missing

Some few months ago I was interviewed by Zacha Rosen in the FBi’s Not What You Think radio show. I was talking about what a galaxy is, the feeling of seeing the center of the Milky Way close to the zenith for the first time, and the problem of the light pollution.

Radio interview in FBI Sydney

The show was broadcasted on FBI 94.5 FM at 10:30am Saturday October 22nd, Sydney time. It is also available as podcast from the Not What You Think webpage or using iTunes.

You can also listen to the 18 minutes interview here:

 

Thanks Zacha for this wonderful experience I hope to repeat in the future!

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:

Spiral galaxy NGC 4027 with AAT: an outreach exercise

During this week I’m curator of the @astrotweep, a Twitter account that each week features an astronomer or planetary scientist taking about their research, science and life. I’m having a lot of fun with it, although I have to recognize it is extra work.

I chose to do it this week because there are some few things happening. In particular, I’m supporting observations at the Anglo-Australian Telescope (Siding Spring Observatory, NSW, Australia) using the 2dF / HERMES instruments. I thought it would be nice to be tweeting life how observations are doing. And that is precisely what I’ve doing today.

On top of that, “this morning” I had an idea. As we always have some “free time” at the AAT after completing the “2dF first night setup” (1) I decided to observe a nice bright deep sky object and get a nice image with the AAT. I was starting to search for a suitable target, but then I though, why don’t I ask the public what do they want to observe?

After consulting with my supervisors and getting the OK to do this, I initiated a poll in both @astrotweeps and @AAOastro asking the public to vote for one of the four following astro objects:

  1. The elliptical galaxy NGC 2865.
  2. The planetary nebula NGC 4361.
  3. The warped and almost edge-on spiral galaxy ESO 510-G13.
  4. The barred spiral galaxy NGC 4027.

For around 8 hours people were casting their vote, we received 153 unique votes in total combining the @AAOastro and the @astrotweets accounts.

And the winner (2) was… the barred spiral galaxy NGC 4027!

But surprises didn’t end here. In the afternoon, when I was starting to prepare the instruments for the night (I’m conducting observations remotely from Sydney), I explained to astronomers and technicians at the AAT what we were doing. Rob Paterson, our afternoon technician, then told me “Do you know we already have the new CCD camera installed in 2dF and just waiting for testing it?

Let me explain why I was so excited when I heard this. For years the 2dF instrument has had an auxiliary camera, the FPI camera, that we use for properly positioning 2dF in the requested field. Rarely it has been used for science, as it is just a 516×516 pixels camera without filters. Occasionally I have also used it for getting some images of deep sky objects. But, as it has no filters, I had to get the color of the images elsewhere, usually taking archive data taken with other telescopes. But the new CCD camera in 2dF does have filters!

Rob phoned Steve Lee, the head of the Night Assistants at the AAT, and with Bob Dean the three of them managed to prepare CACTI (that is the name of the new camera) to have it ready for us.

Although there is still a lot to be done and tests to be conducted, the very first images I got this evening are quite promising. Here is the final result:

Spiral galaxy NGC 4027 located at around 75 million light years in Corvus (The Crow). This barred spiral galaxy, also identified as Arp 22, is identified as a peculiar galaxy by the extended arm, thought to be the result of a collision with another galaxy millions of years ago. This image is the “First Light” of the new CACTI camera in 2dF @ 3.9m Anglo-Australian Telescope. Color image using B (4 x 120 s, blue) + V (6 x 60 s, green) + R (6 x 60 s, red) filters. The data were taken on 11 May 2016 as part of an “outreach exercise” via social media. Click here to get a higher resolution image. Credit: Ángel R. López-Sánchez (AAO/MQ) & Steve Lee, Robert Paterson & Robert Dean (AAO). Night assistant at the AAT: Andre Phillips (AAO).

Note that this image, that actually is the “first light” of the CACTI camera, only combines 6 minutes in V and R and 8 minutes in B, that is, it is not deep at all. Furthermore not extra calibrations were taken (some flatfield images would have been nice). The deep image obtained by the 3.6m NTT telescope (ESO La Silla Observatory, Chile) provides many more details and resolution… but of course they were using the EFOSC instrument, which was specifically designed for deep imaging in optical filters. And the  image of NGC 4027 obtained by David Malin (AAO) using photographic plates at the AAT in 1982 is much more colorful.

But I still think it is a pretty result, particularly as this new image of NGC 4027 was obtained as a completely improvised “outreach exercise” using social media, in which 153 people voted for their favorite object to be observed at the 3.9m Anglo-Australian Telescope.

I really hope to repeat this exercise soon.

(1) A 2dF Plate must be configured with a scientific field, that is, allocating ~350 optical fibres to different objects in the sky. This takes ~ 20-30 minutes.

(2) Just to provide the details of the votes, see table below:

OBJECT    @Astrotweeps   @AAOastro       COMBINED

NGC 2865               5                  4                    9    ( 6% )

NGC 4361            36                   9                   45   (29%)

ESO 510-G13      36                  7                     43   (28%)

NGC 4027           36                20                    56   (37%)

TOTAL              113                 40                   153

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.

Light and Astrophysics: My post for the IYL15 blog

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.

Post originally published on 17th March 2015 in the International Year of Astronomy 2015 (IYL15) blog with the title Light and Astrophysics. The Spanish version of this article was published in Naukas.com.

Unlike the rest of sciences, Astrophysics is not based on carefully experiments designed in a laboratory but in the direct observation of the Universe. Astrophysicists get their data via the analysis of the light we receive from the Cosmos. For achieving this we use extremely sensitive instruments that collect the light emitted by planets, stars, nebulae and galaxies. Certainly, there are some alternative ways to study the Universe besides using the light, as analyzing meteorites or moon rocks, detecting energetic particles such as cosmic rays and neutrinos, or perhaps even using gravitational waves if they actually exist. But the main tool astrophysicists have today to investigate the Cosmos is the study of the radiation we receive from the outer space. Light is the key piece of the Astrophysics we make today.

As the aim is to observe the very faint light coming from objects located even billions of light years away, astronomical observatories are built in relatively isolated places, which are typically located high over the sea level. To observe the Universe, we astrophysicists need dark skies that are not affected by the nasty light pollution created by our society. The inadequate use of the artificial light emitted by streetlight of the cities induces an increasing of the brightness of the night sky. This happens as a consequence of the reflection and diffusion of the artificial light in the gases and particles of dust of the atmosphere. Besides the huge economic waste that it means, light pollution also has a very negative impact on the ecosystem, increases the amount of greenhouse gases in the atmosphere, and drastically diminishes the visibility of the celestial bodies. Unfortunately the light pollution is the reason that a large part of the mankind cannot enjoy a dark starry sky. How is the firmament when we observe it from a dark place? This time-lapse video shows as an example the sky over Siding Spring Observatory (Australia), where the Anglo-Australian Telescope (AAT), managed by the Australian Astronomical Observatory (AAO) and where I work, is located. The darkness of the sky in this observatory allows us to clearly see with our own eyes the Milky Way (the diffuse band of stars that crosses the sky) and many other celestial bodies such as the Magellanic Clouds, the Orion and Carina nebulae, or the Pleiades and Hyades star clusters.


Movie: Time-lapse video “The Sky over the Siding Spring Observatory”. More information about this video in this post in the blog. Credit: Ángel R. López-Sánchez (AAO/MQ).

On the other hand, after traveling during hundreds, millions, or billions of years throughout the deep space, the information codified in the light that reaches us is disrupted by the atmosphere of the Earth in the last millionth of a second of its trip. Hence professional telescopes are built on the top of the mountains, where the atmosphere is more stable than a sea level. Even though, many times this is not enough: our atmosphere distorts the light coming from space and prevents the identification of objects located very close in the sky. New techniques have been developed for compensating the effect of the atmosphere in the quality of the light we receive from the Cosmos. In particular, the adaptive optics technique induces in real time slight modifications to the shape of the primary mirror of the telescope, and therefore they counteract the distortion created by the atmosphere. In any case, astrophysicists need to direct the light received by the telescope to a detector, which transforms light energy into electric energy. This has been the purpose of the CCD (Charge-Couple Device) chips, firstly used by astronomers, and later popularized in smartphones and digital cameras. Very sophisticated optical systems are built to direct the light from the telescope to the detectors. Some of the systems created to manipulate our collection and processing of light are based on optical fibres. This new technology has created the branch of Astrophotonic. Indeed, the AAO, together with the University of Sydney and Macquarie University (Australia), are pioneers in the field of Astrophotonic. The next video shows how the light from the Cosmos is studied at the AAT. First it is collected using the primary mirror of the telescope, which has a diameter of 4 meters, and then it is sent using optical fibres to a dark room where the AAOmega spectrograph is located. This spectrograph, which is a series of special optics, separates the light into its rainbow spectrum, in a similar way a prism separates white light into a rainbow. The separated light is later focussed onto the CCD detector.


Movie: Rainbow Fingerprints, showing how the light of distant galaxies in collected by the Anglo-Australian Telescope and directed to the AAOmega spectrograph using optical fibres. More information: at the AAO webpages. Credit: Australian Astronomical Observatory (AAO), Movie produced by Amanda Bauer (AAO).

Specifically, this video shows how astrophysicists analyse the light coming from distant galaxies to understand their nature and properties. In particular, the video reveals the final science quality spectra for two different types of galaxies, one spiral (top panel) and one elliptical (bottom panel), using actual data obtained with the AAT and the AAOmega spectrograph. The information codified in the rainbow fingerprint identifies each galaxy unambiguously: distance, star formation history, chemical composition, age, physical properties as the temperature or the density of the diffuse gas, and many more. All this information has been captured within a single ray of light that has travelled hundred of millions of years to reach us. Similarly, the properties of stars (luminosity, mass, temperature, chemical composition, kinematics, …), nebulae, and any other celestial body (planets, comets, asteroids, quasars, …) are analyzed through its light. And studying tiny changes in the amount of light we receive from nearby stars we are now finding thousands of exoplanets in the Milky Way.

The “rainbow fingerprints” video shown before includes only the observations of two galaxies, but actually the AAT is able to observe around 350 objects at the same time. This is achieved using the 2dF robot, which can configure 400 optical fibres within a circular field of view with a diameter of 4 full moons. The majority of the optical fibres are allocated to observe galaxies (or stars), but some few optical fibres are used to get an accurate guiding of the telescope or to obtain important calibration data. With this technology the AAT is a survey machine, and indeed it is a pioneer of galaxy surveys. Around 1/3 of all the galaxy distances known today have been obtained using the AAT. The most recent galaxy survey completed at the AAT is the “Galaxy And Mass Assembly” (GAMA) survey, that has collected the light of more than 300 thousand galaxies located in some particular areas of the sky. The next movie shows the 3D distribution of galaxies in one of the sky areas observed by GAMA. This simulated fly through shows the real positions and images of the galaxies that have been mapped by GAMA. Distances are to scale, but the galaxy images have been enlarged for a viewing pleasure.


Movie: “Fly through of the GAMA Galaxy Catalogue”, showing a detailed map of the Universe where galaxies are in 3D. More information in the Vimeo webpage of the video. Crédito: Made by Will Parr, Dr. Mark Swinbank and Dr. Peder Norberg (Durham University) using data from the SDSS (Sloan Digital Sky Survey) and the GAMA (Galaxy And Mass Assembly) surveys.

However, to really understand what happens in the Universe, astrophysicists use not only the light that our eyes can see (the optical range) but all the other “lights” that make up the electromagnetic spectrum, from the very energetic gamma rays to the radio waves. The light codified in the radio waves is studied using radiotelescopes, many of them located in the surface of the Earth. The study of the light in radio frequencies allows us to detect the diffuse, cold gas existing in and around galaxies, the coldest regions of the interstellar medium and where the stars are formed, and energetic phenomena associated to galaxy nuclei hosting an active super-massive black hole in its centre. Many technological achievements, including the invention of the Wi-Fi, come from Radioastronomy. The study of the infrared, ultraviolet, X ray and gamma ray lights must be done using space telescopes, as the atmosphere of the Earth completely blocks these kinds of radiation. As an example, the next image shows how the nearby spiral galaxy M 101 is seen when we use all the lights of the electromagnetic spectrum. Light in X rays traces the most violent phenomena in the galaxy, which are regions associated to supernova remnants and black holes. The ultraviolet (UV) light marks where the youngest stars (those born less than 100 million years ago) are located. Optical (R band) and near-infrared (H band) lights indicate where the sun-like and the old stars are found. The emission coming from ionized hydrogen (H-alpha) reveals the star-forming regions, that is, the nebulae, in M 101. Mid-infrared (MIR) light comes from the thermal emission of the dust, which has been heated up by the young stars. Finally, the image in radio light (neutral atomic hydrogen, HI, at 21 cm) maps the diffuse, cold, gas in the galaxy.

Imagen: Mosaic showing six different views of the galaxy M 101, each one using a different wavelength. Images credit: X ray data (Chandra): NASA/CXC/JHU/K.Kuntz et al,; UV data(GALEX): Gil de Paz et al. 2007, ApJS, 173, 185; R and Hα data (KPNO): Hoopes et al. 2001, ApJ, 559, 878; Near-Infrared data (2MASS): Jarrett et al. 2003, AJ, 125, 525, 8 microns data (Spitzer): Dale et al. 2009, ApJ, 703, 517; 21cm HI data (VLA): Walter et al. 2008, AJ, 136, 2563, ”The H I Nearby Galaxy Survey”. Credit of the composition: Ángel R. López-Sánchez (AAO/MQ).

In any case, today Astrophysics does not only use observations of the light we collect from the Cosmos, but also includes a prominent theoretical framework. “Experiments” in Astrophysics are somewhat performed using computer simulations, where the laws of Physics, together with some initial conditions, are taken into account. When the computer runs, the simulated system evolves and from there general or particular trends are obtained. These predictions must be later compared with the real data obtained using telescopes. Just to name some few cases, stellar interiors, supernova explosions, and galaxy evolution are modeled through careful and sometimes expensive computer simulations. As an example, the next movie shows a cosmological simulation that follows the development of a spiral galaxy similar to the Milky Way from shortly after the Big Bang to the present time. This computer simulation, that required about 1 million CPU hours to be completed, assumes that the Universe is dominated by dark energy and dark matter. The simulation distinguishes old stars (red colour), young stars (blue colour) and the diffuse gas available to form new stars (pale blue), which is the gas we observe using radiotelescopes. This kind of cosmological simulations are later compared with observations obtained using professional telescopes to progress in our understanding of the Cosmos.

Movie: Computer simulation showing the evolution of a spiral galaxy over about 13.5 billion years, from shortly after the Big Bang to the present time. Colors indicate old stars (red), young stars (white and bright blue) and the distribution of gas density (pale blue); the view is 300,000 light-years across. The simulation ran on the Pleiades supercomputer at NASA’s Ames Research Center in Moffett Field, Calif., and required about 1 million CPU hours. It assumes a universe dominated by dark energy and dark matter. More information about this animation in this NASA website. Credit: F. Governato and T. Quinn (Univ. of Washington), A. Brooks (Univ. of Wisconsin, Madison), and J. Wadsley (McMaster Univ.).

In summary, thanks to the analysis of the light we know where stars, galaxies, and all the other celestial bodies are, what are they made of, how do the move, and more. Actually, much of the research that we astrophysicists do today combines observing and analyzing light coming from very different spectral ranges, X rays, ultraviolet, optical, infrared and radio waves. In many cases, we are using techniques that have been known for only few decades and that are still waiting to be fully exploited. The detailed study of the light coming from the Cosmos will provide new important astronomical discoveries in the nearby future and, at the same time, will impulse new technologies; many of them will be applied in medicine and communications. The light techniques we are developing for Astrophysics will have a direct application to our everyday life and will improve the welfare state of our society, besides deepens the understanding of the vast Universe we all live in.