Archivi tag: massive stars

Massive Stars and the Gaia-ESO Survey

Despite their importance for the star-formation history of the Universe, massive stars are particularly poorly understood. However, thanks to projects such as the ongoing Gaia-ESO Survey (GES) and the VLT-Flames Tarantula Survey (VFTS) progress in the number of massive stars with accurate parameters is rapidly growing.

Continua a leggere Massive Stars and the Gaia-ESO Survey

Annunci

Supernovae in the Local Universe: Celebrating 10,000 Days of Supernova 1987A

Supernovae are a core element of modern astrophysics, providing fundamental insights into stellar evolution, the interstellar medium, astroparticle physics, nucleosynthesis and cosmology. While astronomers now routinely detect enormous number of supernovae every year at increasingly large distances, wide-field surveys and all-sky monitoring are now providing an important new element to such studies: there are a growing number of new supernovae being discovered very close to home. Continua a leggere Supernovae in the Local Universe: Celebrating 10,000 Days of Supernova 1987A

Fast outflows in massive stars

Massive Stars are among the dominant sources of light in galaxies. Their high surface temperature, maintained over several evolutionary phases, implies that most of this light is emitted as ultraviolet photons. Through line scattering and the corresponding momentum transfer, this intense radiation field is able to accelerate fast outflows.  Continua a leggere Fast outflows in massive stars

How initial stars and galaxies formed

A simulation of a galaxy formation. Credit: Jason Tumlinson
Un gruppo di astronomi che si dedicano allo studio delle condizioni fisiche dell’Universo primordiale hanno ottenuto nuovi indizi sui processi di formazione delle prime strutture cosmiche, cioè stelle e galassie, andando ad analizzare la composizione chimica di alcune ‘stelle fossili’ che sono distribuite nelle regioni più esterne ed interne dell’alone galattico.

Continua a leggere How initial stars and galaxies formed

GRB 121024A, observed an unusual gamma-ray afterglow

Gamma-ray burst 121024A, as seen on the day of burst by ESO’s Very Large Telescope (VLT) in Chile. Only a week later the source had faded completely. Credit: Dr Klaas Wiersema, University of Leicester, UK and Dr Peter Curran, ICRAR.

Research from an international team of scientists led by the University of Leicester has discovered for the first time that one of the most powerful events in our Universe, Gamma-Ray Bursts (GRB), behave differently than previously thought. The study, published in the prestigious scientific journal Nature, uses evidence from observation of a GRB to rule out most of the existing theoretical predictions concerning the afterglow of the explosions.

Nature: Circular polarization in the optical afterglow of GRB 121024A

Milky Way gives birth to its most massive star

Gli astronomi hanno assistito, si fa per dire, alla nascita della stella più massiccia della Via Lattea, immersa in una nube scura che dista circa 10.000 anni-luce dalla Terra.

The team used the new ALMA (Atacama Large Millimetre/submillimetre Array) telescope in Chile, the most powerful radio telescope in the world, to view the stellar womb which, at 500 times the mass of the Sun and many times more luminous, is the largest ever seen in our galaxy. The researchers say their observations reveal how matter is being dragged into the centre of the huge gaseous cloud by the gravitational pull of the forming star, or stars, along a number of dense threads or filaments. “The remarkable observations from ALMA allowed us to get the first really in-depth look at what was going on within this cloud“, said lead author Nicolas Peretto, from Cardiff University. “We wanted to see how monster stars form and grow, and we certainly achieved our aim”.

One of the sources we have found is an absolute giant, the largest protostellar core ever spotted in the Milky Way! Even though we already believed that the region was a good candidate for being a massive star-forming cloud, we were not expecting to find such a massive embryonic star at its centre.

“This cloud is expected to form at least one star 100 times more massive than the Sun and up to a million times brighter. Only about one in 10,000 of all the stars in the Milky Way reach that kind of mass“. Different theories exist as to how these massive stars form but the team’s findings lend weight to the idea that the entire cloud core begins to collapse inwards, with material raining in towards the centre to form one or more massive stars. Co-author Professor Gary Fuller, from the University of Manchester, said: “Not only are these stars rare, but their births are extremely rapid and childhood short, so finding such a massive object so early in its evolution in our Galaxy is a spectacular result. Our observations reveal in superb detail the filamentary network of dust and gas flowing into the central compact region of the cloud and strongly support the theory of global collapse for the formation of massive stars“. Team member Ana Duarte-Cabral, from the Université de Bordeaux, said: “Matter is drawn into the centre of the cloud from all directions but the filaments are the regions around the star that contain the densest gas and dust and so these distinct patterns are generated“. Peretto added: “We managed to get these very detailed observations using only a fraction of ALMA’s ultimate potential. ALMA will definitely revolutionise our knowledge of star formation, solving some current problems, and certainly raising new ones“.

University of Manchester: Astronomers witness birth of Milky Way’s most massive star

ALMA: ALMA Prenatal Scan Reveals Embryonic Monster Star

arXiv: Global collapse of molecular clouds as a formation mechanism for the most massive stars

This video starts with a view of the Milky Way and closes in on the constellation of Norma and one of the richest parts of the sky. We see many star clusters and glowing nebulae, but many objects of great interest are hidden by thick clouds of dust and can only be seen at longer wavelengths. The final part of the video shows a new view of the dark cloud SDC 335.579-0.292 using ALMA, the Atacama Large Millimeter/submillimeter Array. These observations have given astronomers the best view yet of a monster star in the proces of forming. Credit: ESO/Nick Risinger (skysurvey.org), DSS, ALMA (ESO/NAOJ/NRAO), NASA/JPL-Caltech/GLIMPSE. Music: movetwo

EWASS 2013

Finland will attend the European Week of Astronomy and Space Science, which is going to be held on 8 – 13 July 2013 in Logomo Centre in Turku, Finland. EWASS is the annual meeting of the EAS. On Saturday, 13 July, is also the Plenary discussion on the ASTRONET Mid-Term Review that is closely connected to the EWASS meeting.

The programme for the EWASS 2013 has now been finalized, but small additions are still possible. The pdf-version of the programme with all the timetables and details can be downloaded here. We are going to print this for the meeting and you will have this during the registration.

Symposia

S1: Solar activity and its manifestations in the heliosphere (PI Rami Vainio)
S2: The physics of accretion on compact objects (PI Juri Poutanen)
S3: Science with Planck data (PI Pekka Heinämäki)
S4: The mystery of ellipticals (PI Peter Johansson)
S5: Local group, local cosmology (PI Matteo Monelli/Stefania Salvadori)
S7: Stellar magnetic activity across the HR diagram (PI Maarit Mantere)
S8: Deaths of massive stars as supernovae and gamma-ray bursts (PI Seppo Mattila)
S9: Extreme physics of neutron stars (PI Dmitry Yakovlev)
S10:The co-evolution of black holes and galaxies (PI Jari Kotilainen)
S11: Gaia research for European astronomy training (PI Nicholas Walton)
S12: The gamma-ray sky in the era of Fermi and Cherenkov telescopes (PI Tuomas Savolainen/Elina Lindfors)

Special sessions

Sp1: Astronomy education and public outreach (PI Mikko Hanski)
Sp2: RADIONET: “The role of modern radio observatories in black hole and jet studies” (F.Mantovani/T. Savolainen/M. Tornikoski)
Sp3: Fundamental stellar parameters (PI Luca Casagrande)
Sp4: The origin of interstellar dust (PI Patrice Bouchet)
Sp5: Thick discs: clues for galaxy formation and evolution (PI Sebastien Comeron)
Sp6: AGN, galaxy mergers, supermassive black holes and gravitational waves (PI Stefanie Komossa/Mauri Valtonen)
Sp7: Science with present and future interferometric instruments (PI Jean Surdej)
Sp8: Galactic molecular clouds and their chemistry (PI Mika Juvela)
Sp9: Stellar dynamics and celestial mechanics in modern astrophysics (PI Rainer Spurzem/Seppo Mikkola)
Sp10: Chemo-dynamical galaxy evolution (PI Gerhard Hensler)
Sp11: Rocks in our Solar System (PI Tomas Kohout)
Sp12: A fresh look at the stellar initial mass function (PI Ignacio Ferreras)
Sp13: Starburst galaxies now and then with ALMA (PI Jari Kotilainen)
Sp14: LOFT, the large observatory for X-ray timing (PI Enrico Bozzo)

New hints on primordial galaxies

Le galassie primordiali avevano un aspetto alquanto differente rispetto a quelle che popolano l’Universo oggi. Grazie ad una serie di osservazioni condotte con il Very Large Telescope (VLT) e il telescopio spaziale Hubble (HST), alcuni ricercatori hanno studiato una galassia molto antica, con una accuratezza senza precedenti, e da cui è stato possibile determinare alcuni parametri astrofisici che la caratterizzano, come la massa, la dimensione, il contenuto chimico e il tasso di formazione stellare.

Galaxies are deeply fascinating objects. The seeds of galaxies are quantum fluctuations in the very early Universe and thus, understanding of galaxies links the largest scales in the Universe with the smallest. It is only within galaxies that gas can become cold and dense enough to form stars and galaxies are therefore the cradles of starsbirths”, explains Johan Fynbo, professor at the Dark Cosmology Centre at the Niels Bohr Institute at the University of Copenhagen. Early in the Universe, galaxies were formed from large clouds of gas and dark matter. Gas is the Universe’s raw material for the formation of stars. Inside galaxies the gas can cool down from the many thousands of degrees it has outside galaxies. When gas is cooled it becomes very dense. Finally, the gas is so compact that it collapses into a ball of gas where the gravitational compresion heats up the matter, creating a glowing ball of gas, a star is born. In the red-hot interior of massive stars, hydrogen and helium melt together and form the first heavier elements like carbon, nitrogen, oxygen, which go on to form magnesium, silicon and iron. When the entire core has been converted into iron, no more energy can be extracted and the star dies as a supernova explosion. Every time a massive star burns out and dies, it hence flings clouds of gas and newly formed elements out into space, where they form gas clouds that get denser and denser and eventually collapse to form new stars. The early stars contained only a thousandth of the elements found in the Sun today. In this way, each generation of stars becomes richer and richer in heavy elements. In today’s galaxies, we have a lot of stars and less gas. In the early galaxies, there was a lot of gas and fewer stars. “We want to understand this cosmic evolutionary history better by studying very early galaxies. We want to measure how large they are, what they weigh and how quickly stars and heavy elements are formed”, explains Johan Fynbo.

The research team has studied a galaxy located approximately 11 billion years back in time in great detail.

Behind the galaxy is a quasar, which is an active black hole that is brighter than a galaxy. Using the light from the quasar, they found the galaxy using the giant telescopes, VLT in Chile. The large amount of gas in the young galaxy simply absorbed a massive amount of the light from the quasar lying behind it. Here they could ‘see’, via absorption, the outer parts of the galaxy. Furthermore, active star formation causes some of the gas to light up, so it could be observed directly. With the Hubble Space Telescope they could also see the recently formed stars in the galaxy and they could calculate how many stars there were in relation to the total mass, which is comprised of both stars and gas. They could now see that the relative proportion of heavier elements is the same in the centre of the galaxy as in the outer parts and it shows that the stars that are formed earlier in the centre of the galaxy enrich the stars in the outer parts with heavier elements. “By combining the observations from both methods – absorption and emission – we have discovered that the stars have an oxygen content equivalent to approx. 1/3 of the Sun’s oxygen content. This means that earlier generations of stars in the galaxy had already built up elements that made it possible to form planets like Earth 11 billion years ago”, conclude Johan Fynbo.

University of Copenaghen: New knowledge about early galaxies
arXiv: Comprehensive Study of a z = 2:35 DLA Galaxy: Mass, Metallicity, Age, Morphology and SFR from HST and VLT

Massive Stars: From alpha to Omega

The ‘Massive Stars’ meetings (poster) have enjoyed more than 40 years of startling success since the first meeting in Argentina in 1971. Held every 4 to 5 years, these meetings aim to encapsulate the current state-of-the-art of our understanding of the physics of Massive Stars and their role in the Universe. For this 10th meeting in the Massive Stars series the Institute of Astronomy, Astrophysics, Space Applications and Remote Sensing of the National Observatory of Athens, invites you to the island of Rhodes, once home to one of the greatest astronomers of antiquity, Hipparchos, who is generally acknowledged as the founder of trigonometry, discoverer of precession and publisher of the first star catalog around 135 BC.

The conference will build on results from ongoing large-scale multi-wavelength surveys of massive stars which are being coupled with new theoretical advances dealing with stellar evolution and the processes which affect that evolution: mass-loss, rotation, convection, magnetic fields, multiplicity and environment. It will tackle important problems from birth, through main sequence evolution and until core collapse. There will be a strong focus on relating the major theoretical uncertainties afflicting stellar evolution through these phases to the current observational picture. The impetus for this focus is derived from the realization that our understanding of massive star evolution is severely challenged by new observations powered largely by technological advances in telescopes and instrumentation. This has enabled new ways of looking at old long-standing problems enabling large-scale high-quality surveys of resolved stellar populations. As theoretical approaches try to keep pace with this increase in information the cracks in our assumptions concerning stellar evolution have become more apparent, even glaring. Whereas before it might have been possible to understand some of the stars some of the time it is now clear that understanding stellar populations is a considerable challenge and will require substantial efforts to resolve. This is an exciting time as observations have revealed large gaps in understanding of the formation and evolution of massive stars. The huge impact that massive stars have on their immediate environment, parent galaxies, and through the Universe, demands better understanding of massive star evolution from alpha to Omega.