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💫NGC 922

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Episode 60 of the Hubblecast explores NGC 922, a galaxy that has been hit square-on by another.



Ripples of star-formation are still propagating out across thousands of light-years of space over 300 million years after the collision, making it a prime example of what astronomers call a collisional ring galaxy.


Credit: NASA & ESA


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💫Las muchas caras de Abell 1758

Norte, este, sur, oeste: Las muchas caras de Abell 1758

Fecha: 18 de enero de 2018

Fuente: ESA / Hubble Information Center

Resumen:
Parecido a un enjambre de luciérnagas parpadeantes, este hermoso cúmulo de galaxias brilla intensamente en el oscuro cosmos, acompañado por la miríada de brillantes luces de estrellas en primer plano y galaxias espirales en espiral. A1758N es un subgrupo de Abell 1758, un cúmulo masivo que contiene cientos de galaxias. Aunque puede parecer sereno en esta imagen del Telescopio Espacial Hubble de la NASA / ESA, el subgrupo en realidad comprende dos estructuras aún más pequeñas actualmente en el proceso turbulento de fusión.
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💫Baby galaxy is not so young after all


Observations of I Zwicky 18 at the Palomar Observatory around 40 years ago seemed to show that it was one of the youngest galaxies in the nearby Universe. The studies suggested that the galaxy had erupted with star formation billions of years after its galactic neighbours, like our galaxy the Milky Way. Back then it was an important finding for astronomers, since this young galaxy was also nearby and could be studied in great detail; something that is not possible with observations made across great distances when the universe was much younger. But these new Hubble data have quashed that possibility. The telescope found fainter older red stars contained within the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as 10 billion years ago. The galaxy, therefore, may have formed at the same time as most other galaxies. "Although the galaxy is not as youthful as was once believed, it is certainly developmentally challenged and unique in the nearby Universe," said astronomer Alessandra Aloisi from the European Space Agency/Space Telescope Science Institute, who led the new study. Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is mostly composed of hydrogen and helium, the main ingredients created in the Big Bang. In other words the stars within it have not created the same amounts of heavier elements as seen in other galaxies nearby.

Thus the galaxy's primordial makeup suggests that its rate of star formation has been much lower than that of other galaxies of similar age. The galaxy has been studied with most of NASA's telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, and the Far Ultraviolet Spectroscopic Explorer (FUSE). However, it remains an outstanding mystery why I Zwicky 18 formed so few stars in the past, and why it is forming so many new stars right now. The new Hubble data also suggest that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. On extragalactic standards this is still in our own backyard yet the galaxy's larger-than-expected distance may now explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint old stars in I Zwicky 18 are almost at the limit of Hubble's sensitivity and resolution. Aloisi and her team discerned the new distance by observing blinking stellar distance-markers within I Zwicky 18.

These massive stars, called Cepheid variables, pulse with a regular rhythm. The timing of their pulsations is directly related to their brightness. By comparing their actual brightness with their observed brightness, astronomers can precisely measure their distance. The team determined the observed brightness of three Cepheids and compared it to the actual brightness predicted by theoretical models specifically calculated for the low metal content of I Zwicky 18 in order to determine the galaxy's distance. The Cepheid distance was also validated through another distance indicator, specifically the observed brightness of the brightest red stars in a characteristic stellar evolutionary phase (the so-called "giant" phase). Cepheid variable stars have been studied for decades (especially by Hubble) and have been instrumental in the determination of the scale of our universe. This is the first time, however, that variable stars with so few heavy elements were found. This may provide unique new insights into the properties of variable stars, which is now a topic of ongoing study.

Credit:
NASA, ESA, and A. Aloisi (European Space Agency and Space Telescope Science Institute)


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💫Field of view of NGC 2440

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This is a 3°x3° field of view of NGC 2440 region, taken by a ground-based telescope. This image, just taken by the NASA/ESA Hubble Space Telescope, shows the colourful "last hurrah" of a star like our Sun. The star is ending its life by casting off its outer layers of gas, which formed a cocoon around the star's remaining core. Ultraviolet light from the dying star makes the material glow. The burned-out star, called a white dwarf, is the white dot in the centre. Our Sun will eventually burn out and shroud itself with stellar debris, but not for another 5 billion years. Our Milky Way Galaxy is littered with these stellar relics, called planetary nebulae. The objects have nothing to do with planets. Eighteenth- and nineteenth-century astronomers called them the name because through small telescopes they resembled the disks of the distant planets Uranus and Neptune.



The planetary nebula in this image is called NGC 2440. The white dwarf at the centre of NGC 2440 is one of the hottest known, with a surface temperature of more than 200,000 degrees Celsius. The nebula's chaotic structure suggests that the star shed its mass episodically. During each outburst, the star expelled material in a different direction. This can be seen in the two bowtie-shaped lobes. The nebula also is rich in clouds of dust, some of which form long, dark streaks pointing away from the star. NGC 2440 lies about 4,000 light-years from Earth in the direction of the constellation Puppis.




Credit: Digitized Sky Survey 2 / NASA, ESA, and K. Noll (STScI)


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💫Movimiento de Whirlpool en las primeras galaxias

Los astrónomos detectan el movimiento de torbellinos en las primeras galaxias

Publicado ayer

Los astrónomos han mirado atrás a un tiempo poco después del Big Bang, y han descubierto el remolino de gas en algunas de las primeras galaxias que se formaron en el Universo. Estos 'recién nacidos' - observados como aparecieron hace casi 13 mil millones de años - giraron como un remolino, similar a nuestra propia Vía Láctea.



💫Large and small stars in harmonious coexistence


This is a Hubble Space Telescope image of one of the hundreds of star-forming stellar systems, called stellar associations, located 180,000 light-years away in the Large Magellanic Cloud (LMC). The LMC is the second closest known satellite galaxy of our Milky Way, orbiting it roughly every 1.5 billion years. Earlier ground-based observations of such systems had only allowed astronomers to study the bright blue giant stars in these systems, and not the low-mass stars. This new, most detailed view to date of the star-forming association LH 95 was taken with Hubble's Advanced Camera for Surveys and provides a extraordinarily rich sample of newly formed low-mass stars, allowing a more accurate calculation of their ages and masses. An international team of astronomers, led by Dimitrios Gouliermis of the Max-Planck Institute for Astronomy (MPIA) in Heidelberg, is currently studying the Hubble data. According to Dr. Gouliermis "Hubble's sharp vision has over the years dramatically changed the picture that we had for stellar associations in the Magellanic Clouds". The LMC is a galaxy with relatively small amounts of elements heavier than hydrogen, giving astronomers an insight into star-formation in environments different from our Milky Way.

Once massive stars - those with at least 3 times the mass of the Sun - have formed, they generate strong stellar winds and high levels of ultraviolet radiation that ionize the surrounding interstellar gas. The result is a nebula of glowing hydrogen that will expand out into the molecular cloud that originally collapsed to form these stars. The blue haze seen throughout the image around LH 95 is actually part of this bright nebula, known as DEM L 252. Some dense parts of this star-forming region have not been completely eroded by the stellar winds and can still be seen as dark dusty filaments in the picture. Such dust lanes absorb parts of the blue light from the stars behind them, making them appear redder. Other parts of the molecular cloud have already contracted to turn into glowing groups of infant stars, the fainter of which have a high tendency to cluster. The new Hubble view of LH 95 shows that there are at least two small compact clusters associated with such groups, one to the right, above the centre of the picture and one to the far left. These stellar nurseries host hundreds of newly discovered infant low-mass stars. Such stars have also been found by Hubble in the main part of LH 95 amongst its massive bright stellar members.

Credit:
Davide De Martin (ESA/Hubble), the ESA/ESO/NASA Photoshop FITS Liberator & Digitized Sky Survey 2


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