The latest report from the European Southern Observatory (ESO):

A Fleeting Moment in Time
European Southern Observatory’s Cosmic Gems Programme
captures last breath of a dying star

The faint, ephemeral glow emanating from the planetary nebula ESO 577-24 persists for only a short time — around 10,000 years, a blink of an eye in astronomical terms. ESO’s Very Large Telescope captured this shell of glowing ionised gas — the last breath of the dying star whose simmering remains are visible at the heart of this image. As the gaseous shell of this planetary nebula expands and grows dimmer, it will slowly disappear from sight.

An evanescent shell of glowing gas spreading into space — the planetary nebula ESO 577-24 —  dominates this image [1]. This planetary nebula is the remains of a dead giant star that has thrown off its outer layers, leaving behind a small, intensely hot dwarf star. This diminished remnant will gradually cool and fade, living out its days as the mere ghost of a once-vast red giant star.

Red giants are stars at the end of their lives that have exhausted the hydrogen fuel in their cores and begun to contract under the crushing grip of gravity. As a red giant shrinks, the immense pressure reignites the core of the star, causing it to throw its outer layers into the void as a powerful stellar wind. The dying star’s incandescent core emits ultraviolet radiation intense enough to ionise these ejected layers and cause them to shine. The result is what we see as a planetary nebula — a final, fleeting testament to an ancient star at the end of its life [2].

This dazzling planetary nebula was discovered as part of the National Geographic Society  — Palomar Observatory Sky Survey in the 1950s, and was recorded in the Abell Catalogue of Planetary Nebulae in 1966 [3]. At around 1400 light years from Earth, the ghostly glow of ESO 577-24 is only visible through a powerful telescope. As the dwarf star cools, the nebula will continue to expand into space, slowly fading from view.

This image of ESO 577-24 was created as part of the ESO Cosmic Gems Programme, an initiative that produces images of interesting, intriguing, or visually attractive objects using ESO telescopes for the purposes of education and public outreach. The programme makes use of telescope time that cannot be used for scientific observations; nevertheless, the data collected are made available to astronomers through the ESO Science Archive.

Notes

[1] Planetary nebulae were first observed by astronomers in the 18th century — to them, their dim glow and crisp outlines resembled planets of the Solar System.

[2] By the time our Sun evolves into a red giant, it will have reached the venerable age of 10 billion years. There is no immediate need to panic, however — the Sun is currently only 5 billion years old.

[3] Astronomical objects often have a variety of official names, with different catalogues providing different designations. The formal name of this object in the Abell Catalogue of Planetary Nebulae is PN A66 36.

More information

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It has 16 Member States: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and with Australia as a Strategic Partner. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its world-leading Very Large Telescope Interferometer as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. ESO is also a major partner in two facilities on Chajnantor, APEX and ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre Extremely Large Telescope, the ELT, which will become “the world’s biggest eye on the sky”.

Links

• Cosmic Gems Programme
• More information on the VLT
• More information on FORS
• Images of the VLT

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Einstein’s Monsters: The Life and Times of Black Holes

The Hubble Space Telescope collaboration has released huge new mosaic image of the Trangulum Galaxy:

Hubble takes gigantic image of the Triangulum Galaxy

The NASA/ESA Hubble Space Telescope has captured the most detailed image yet of a close neighbour of the Milky Way — the Triangulum Galaxy, a spiral galaxy located at a distance of only three million light-years. This panoramic survey of the third-largest galaxy in our Local Group of galaxies provides a mesmerising view of the 40 billion stars that make up one of the most distant objects visible to the naked eye.

This video journey takes the viewer on a three-million-light-year trip to the Triangulum Galaxy, Messier 33. The final view, from the NASA/ESA Hubble Space Telescope, is the most detailed wide-field view of this object ever obtained and shows the many glowing gas clouds in the spiral arms with particular clarity. Credit:ESA, ESO, DSS, NASA, Risinger. Music: Astral Electronic

This new image of the Triangulum Galaxy — also known as Messier 33 or NGC 598 — has a staggering 665 million pixels and showcases the central region of the galaxy and its inner spiral arms. To stitch together this gigantic mosaic, Hubble’s Advanced Camera for Surveys needed to create 54 separate images.

Under excellent dark-sky conditions, the Triangulum Galaxy can be seen with the naked eye as a faint, blurry object in the constellation of Triangulum (the Triangle), where its ethereal glow is an exciting target for amateur astronomers.

At only three million light-years from Earth, the Triangulum Galaxy is a notable member of the Local Group — it is the group’s third-largest galaxy, but also the smallest spiral galaxy in the group [1]. It measures only about 60 000 light-years across, compared to the 200 000 light-years of the Andromeda Galaxy; the Milky Way lies between these extremes at about 100 000 light-years in diameter [2].

The Triangulum Galaxy is not only surpassed in size by the other two spirals, but by the multitude of stars they contain. The Triangulum Galaxy has at least an order of magnitude less stars than the Milky Way and two orders of magnitude less than Andromeda. These numbers are hard to grasp when already in this image 10 to 15 million individual stars are visible.

In contrast to the two larger spirals, the Triangulum Galaxy doesn’t have a bright bulge at its centre and it also lacks a bar connecting its spiral arms to the centre. It does, however, contain a huge amount of gas and dust, giving rise to rapid star formation. New stars form at a rate of approximately one solar mass every two years.

The abundance of gas clouds in the Triangulum Galaxy is precisely what drew astronomers to conduct this detailed survey. When stars are born, they use up material in these clouds of gas and dust, leaving less fuel for new stars to emerge. Hubble’s image shows two of the four brightest of these regions in the galaxy: NGC 595 and NGC 604. The latter is the second most luminous region of ionised hydrogen within the Local Group and it is also among the largest known star formation regions in the Local Group.

These detailed observations of the Triangulum Galaxy have tremendous legacy value — combined with those of the Milky Way, the Andromeda Galaxy and the irregular Magellanic Cloud galaxies, they will help astronomers to better understand star formation and stellar evolution.

Notes

[1] Our galaxy, the Milky Way, is part of the Local Group, an assembly of more than 50 galaxies bound together by gravity. Its largest member is the Andromeda Galaxy — also known as Messier 31 — followed by the Milky Way and the Triangulum Galaxy. The remaining members of the Local Group are dwarf galaxies, each orbiting one of the three larger ones.

[2] The much bigger Andromeda Galaxy was mapped by Hubble in 2015, creating the sharpest and largest image of this galaxy and the largest Hubble image ever (heic1502).

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.

Image credit: NASA, ESA

Links

• Images of Hubble
• Hubblesite release

A preview from NASA JPL of the December night sky:

And here is more from the Hubble Space Telescope Institute:

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Einstein’s Monsters: The Life and Times of Black Holes

 

A new report from ESO (European Southern Observatory):

Cosmic Serpent
ESO’s VLT captures details of an elaborate serpentine system
sculpted by colliding stellar winds

The VISIR instrument on ESO’s Very Large Telescope has captured this stunning image of a newly discovered massive triple star system. Nicknamed Apep after an ancient Egyptian deity, this may be the first ever gamma-ray burst progenitor found.

This serpentine swirl, captured by the VISIR instrument on ESO’s Very Large Telescope (VLT), has an explosive future ahead of it; it is a Wolf-Rayet star system, and a likely source of one of the most energetic phenomena in the Universe — a long-duration gamma-ray burst (GRB).

“This is the first such system to be discovered in our own galaxy,” explains Joseph Callingham of the Netherlands Institute for Radio Astronomy (ASTRON), lead author of the study reporting this system. “We never expected to find such a system in our own backyard” [1].

The system, which comprises a nest of massive stars surrounded by a “pinwheel” of dust, is  officially known only by unwieldy catalogue references like 2XMM J160050.7-514245. However, the astronomers chose to give this fascinating object a catchier moniker — “Apep”.

Apep got its nickname for its sinuous shape, reminiscent of a snake coiled around the central stars. Its namesake was an ancient Egyptian deity, a gargantuan serpent embodying chaos — fitting for such a violent system. It was believed that Ra, the Sun god, would battle with Apep every night; prayer and worship ensured Ra’s victory and the return of the Sun.

GRBs are among the most powerful explosions in the Universe. Lasting between a few thousandths of a second and a few hours, they can release as much energy as the Sun will output over its entire lifetime. Long-duration GRBs — those which last for longer than 2 seconds — are believed to be caused by the supernova explosions of rapidly-rotating Wolf-Rayet stars.

Some of the most massive stars evolve into Wolf-Rayet stars towards the end of their lives. This stage is short-lived, and Wolf-Rayets survive in this state for only a few hundred thousand years — the blink of an eye in cosmological terms. In that time, they throw out huge amounts of material in the form of a powerful stellar wind, hurling matter outwards at millions of kilometres per hour; Apep’s stellar winds were measured to travel at an astonishing 12 million km/h.

These stellar winds have created the elaborate plumes surrounding the triple star system — which consists of a binary star system and a companion single star bound together by gravity. Though only two star-like objects are visible in the image, the lower source is in fact an unresolved binary Wolf-Rayet star. This binary is responsible for sculpting the serpentine swirls surrounding Apep, which are formed in the wake of the colliding stellar winds from the two Wolf-Rayet stars.

Compared to the extraordinary speed of Apep’s winds, the dust pinwheel itself swirls outwards at a leisurely pace, “crawling” along at less than 2 million km/h. The wild discrepancy between the speed of Apep’s rapid stellar winds and that of the unhurried dust pinwheel is thought to result from one of the stars in the binary launching both a fast and a slow wind — in different directions.

This would imply that the star is undergoing near-critical rotation — that is, rotating so fast that it is nearly ripping itself apart. A Wolf-Rayet star with such rapid rotation is believed to produce a long-duration GRB when its core collapses at the end of its life.

Notes
[1] Callingham, now at the Netherlands Institute for Radio Astronomy (ASTRON), did part of this research while at the University of Sydney working with research team leader Peter Tuthill. In addition to observations from ESO telescopes, the team also used the Anglo-Australian Telescope at Siding Spring Observatory, Australia.

Links

• Research paper
• Photos of the VLT
• Behind the Paper blog post