Archivi tag: galaxy mergers

Le galassie della serie… ‘rosse e inattive’!

Da sempre, gli astronomi stanno cercando di capire come mai le galassie giovani, dette starburst cioè quelle che stanno formando rapidamente nuove stelle ad un ritmo almeno 100 volte superiore rispetto alla Via Lattea, arrestano quei processi di formazione stellare per entrare a far parte di una categoria che gli scienziati chiamano “quelle rosse e inattive”. In genere, le galassie starburst derivano dalla fusione o dall’incontro ravvicinato di due galassie. In precedenza, alcune osservazioni di queste galassie hanno rivelato getti di gas verso l’esterno che si propagano con velocità dell’ordine di 3 milioni di chilometri all’ora. Ma agli astronomi mancava la prova diretta di ciò che espelle il gas, l’ingrediente fondamentale per la creazione di nuove stelle. Ora un gruppo di ricercatori, guidati da Gregory Rudnick dell’University of Kansas, ritengono di aver trovato alcune risposte al perchè le galassie giovani e compatte diventano una sorta di “rovine galattiche”. Grazie ad una serie di osservazioni condotte con i telescopi spaziali Hubble e Chandra, gli astronomi hanno trovato che l’energia prodotta dagli stessi processi di formazione stellare crea una mancanza di gas all’interno delle galassie starbust determinando perciò un arresto alla formazione di nuove stelle. I risultati di questo studio sono stati pubblicati su Monthly Notices of the Royal Astronomical Society.

University of Kansas: Research reveals the real cause of death for some starburst galaxies 

arXiv: Massive Compact Galaxies with High-Velocity Outflows: Morphological Analysis and Constraints on AGN Activity

Pubblicità

Seeds of supermassive black holes are quite massive themselves

The galaxy NGC 4395 is shown here in infrared light, captured by NASA’s Spitzer Space Telescope. This dwarf galaxy is relatively small in comparison with our Milky Way galaxy, which is nearly 1,000 times more massive. Image Credit: NASA/JPL-Caltech
Come fa un buco nero supermassiccio ad acquisire una massa che va tipicamente da qualche decina/centinaia di milioni fino a qualche miliardo di masse solari? Ad oggi, non c’è una risposta ben precisa ma alcuni dati ottenuti di recente dal telescopio spaziale Wide-field Infrared Survey Explorer (WISE) stanno facendo luce sulla natura di quei “siti cosmici” dove hanno origine i buchi neri. Inoltre, questi dati forniscono nuovi indizi che hanno lo scopo di comporre insieme il puzzle che descrive l’evoluzione di questi enigmatici oggetti che risiedono nei nuclei delle galassie attive.

Growing a black hole is not as easy as planting a seed in soil and adding water. The massive objects are dense collections of matter that are literally bottomless pits; anything that falls in will never come out. They come in a range of sizes. The smallest, only a few times greater in mass than our Sun, form from exploding stars. The biggest of these dark beasts, billions of times the mass of our Sun, grow together with their host galaxies over time, deep in the interiors. But how this process works is an ongoing mystery. Researchers using WISE addressed this question by looking for black holes in smaller, “dwarf” galaxies. These galaxies have not undergone much change, so they are more pristine than their heavier counterparts. In some ways, they resemble the types of galaxies that might have existed when the Universe was young, and thus they offer a glimpse into the nurseries of supermassive black holes. In this new study, using data of the entire sky taken by WISE in infrared light, up to hundreds of dwarf galaxies have been discovered in which buried black holes may be lurking. Infrared light, the kind that WISE collects, can see through dust, unlike visible light, so it’s better able to find the dusty, hidden black holes. The researchers found that the dwarf galaxies’ black holes may be about 1,000 to 10,000 times the mass of our Sun, larger than expected for these small galaxies. “Our findings suggest the original seeds of supermassive black holes are quite massive themselves“, said Shobita Satyapal of George Mason University, Fairfax, Va.

Daniel Stern, an astronomer specializing in black holes at NASA’s Jet Propulsion Laboratory, Pasadena, California, who was not a part of the new study, says: “The research demonstrates the power of an all-sky survey like WISE to find the rarest black holes. Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack“.

The new observations argue against one popular theory of black hole growth, which holds that the objects bulk up in size through galaxy collisions.

When our Universe was young, galaxies were more likely to crash into others and merge. It is possible the galaxies’ black holes merged too, accumulating more mass. In this scenario, supermassive black holes grow in size through a series of galaxy mergers. The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don’t have a history of galactic smash-ups, and yet their black holes are already relatively big. Instead, supermassive black holes might form very early in the history of the Universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas.”We still don’t know how the monstrous black holes that reside in galaxy centers formed“, said Satyapal. “But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early Universe, before galaxies collided with other galaxies“.

NASA: The Search for Seeds of Black Holes

arXiv: Discovery of a Population of Bulgeless Galaxies with Extremely Red Mid-IR Colors: Obscured AGN Activity in the Low Mass Regime?

 

 

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)