Saturday, November 18, 2017

Astronomers Discover A Star That Would Not Die

Artist’s impression of a Supernova
Credit: NASA/ESA/G. Bacon (STSci)

iPTF14hls ​grew ​bright ​and ​dim ​again ​at ​least ​five ​times ​over ​two ​years. ​This ​behavior ​has ​never ​been seen ​in ​previous ​supernovae, ​which ​typically ​remain ​bright ​for approximately 100 days and ​then fade. Adapted from Arcavi et ​al. 2017, ​Nature. Credit: LCO/S. ​Wilkinson

An image taken ​by ​the ​Palomar ​Observatory ​Sky Survey ​reveals ​a ​possible ​explosion ​in the ​year ​1954 ​at the ​location ​of ​iPTF14hls ​(left), ​not ​seen ​in ​a ​later ​image ​taken ​in ​1993 ​(right). ​Supernovae ​are ​known ​to explode only ​once, ​shine ​for ​a ​few ​months ​and ​then fade, ​but ​iPTF14hls ​experienced ​at ​least ​two explosions, 60 ​years ​apart. Adapted ​from Arcavi et ​al. ​2017, ​Nature.

Lead author Iair​ ​Arcavi,​ ​a​ ​NASA​ ​Einstein​ ​postdoctoral​ ​fellow​ ​at​ ​LCO​ ​and​ ​the​ ​University​ ​of​ ​California Santa​ ​Barbara, visiting the Keck Observatory twin 10-meter optical/infrared telescopes on Maunakea, Hawaii. Credit: I. Arcavi



Maunakea, Hawaii – An international team of astronomers led by Las Cumbres Observatory (LCO) has made a bizarre discovery; a star that refuses to stop shining.

Supernovae, the explosions of stars, have been observed in the thousands and in all cases they marked the death of a star.

But in a study published today in the journal Nature, the team discovered a remarkable exception; a star that exploded multiple times over a period of more than fifty years. Their observations, which include data from W. M. Keck Observatory on Maunakea, Hawaii, are challenging existing theories on these cosmic catastrophes.

“The spectra we obtained at Keck Observatory showed that this supernova looked like nothing we had ever seen before. This, after discovering nearly 5,000 supernovae in the last two decades,” said Peter Nugent, Senior Scientist and Division Deputy for Science Engagement in the Computational Research Division at Lawrence Berkeley National Laboratory who co-authored the study. “While the spectra bear a resemblance to normal hydrogen-rich core-collapse supernova explosions, they grew brighter and dimmer at least five times more slowly, stretching an event which normally lasts 100 days to over two years.”

Researchers used the Low Resolution Imaging Spectrometer (LRIS) on the Keck I telescope to obtain spectrum of the star’s host galaxy, and the Deep Imaging and Multi-Object Spectrograph (DEIMOS) on Keck II to obtain high-resolution spectra of the unusual star itself.

The supernova, named iPTF14hls, was discovered in September of 2014 by the Palomar Transient Factory. At the time, it looked like an ordinary supernova. Several months later, LCO astronomers noticed the supernova was growing brighter again after it had faded.

When astronomers went back and looked at archival data, they were astonished to find evidence of an explosion in 1954 at the same location. This star somehow survived that explosion and exploded again in 2014.

“This supernova breaks everything we thought we knew about how they work. It’s the biggest puzzle I’ve encountered in almost a decade of studying stellar explosions,” said lead author Iair Arcavi, a NASA Einstein postdoctoral fellow at LCO and the University of California Santa Barbara.

The study calculated that the star that exploded was at least 50 times more massive than the sun and probably much larger. Supernova iPTF14hls may have been the most massive stellar explosion ever seen. The size of this explosion could be the reason that our conventional understanding of the death of stars failed to explain this event.

Supernova iPTF14hls may be the first example of a “Pulsational Pair Instability Supernova.”

“According to this theory, it is possible that this was the result of star so massive and hot that it generated antimatter in its core,” said co-author Daniel Kasen, an associate professor in the Physics and Astronomy Departments at UC Berkeley and a scientist at Lawrence Berkeley Lab. “That would cause the star to go violently unstable, and undergo repeated bright eruptions over periods of years.”

That process may even repeat over decades before the star’s large final explosion and collapse to a black hole.

“These explosions were only expected to be seen in the early universe and should be extinct today. This is like finding a dinosaur still alive today. If you found one, you would question whether it truly was a dinosaur,” said Andy Howell, leader of the LCO supernova group and co-author of the study.

Indeed, the “Pulsational Pair Instability” theory may not fully explain all the data obtained for this event. For example, the energy released by the supernova is more than the theory predicts. This supernova may be something completely new.

Astronomers continue to monitor iPTF14hls, which remains bright three years after it was discovered.

“This is one of those head-scratcher type of events,” said Nugent. “At first we thought it was completely normal and boring. Then it just kept staying bright, and not changing, for month after month. Piecing it all together, from our observations at Palomar Transient Factory, Keck Observatory, LCOGT, and even the images from 1954 in the Palomar Sky Survey, has started to shed light on what this could be. I would really like to find another one like this.”


Media Contact:

Mari-Ela Chock, Communications Officer
mchock@keck.hawaii.edu
(808) 554-0567





About W.M. Keck Observatory

The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems.

Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

Friday, November 17, 2017

Cosmic search for a missing limb

Credit: ESA/Hubble & NASA


This new Picture of the Week, taken by the NASA/ESA Hubble Space Telescope, shows the dwarf galaxy NGC 4625, located about 30 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The image, acquired with the Advanced Camera for Surveys (ACS), reveals the single spiral arm of the galaxy, which gives it an asymmetric appearance. But why is there only one spiral arm, when spiral galaxies normally have at least two?

Astronomers looked at NGC 4625 in different wavelengths in the hope of solving this cosmic mystery. Observations in the ultraviolet provided the first hint: in ultraviolet light the disc of the galaxy appears four times larger than on the image depicted here. An indication that there are a large number of very young and hot — hence mainly visible in the ultraviolet — stars forming in the outer regions of the galaxy. These young stars are only around one billion years old, about 10 times younger than the stars seen in the optical centre. At first astronomers assumed that this high star formation rate was being triggered by the interaction with another, nearby dwarf galaxy called NGC 4618.

They speculated that NGC 4618 may be the culprit “harassing” NGC 4625, causing it to lose all but one spiral arm. In 2004 astronomers found proof for this claim: The gas in the outermost regions of the dwarf galaxy NGC 4618 has been strongly affected by NGC 4625.



Thursday, November 16, 2017

Closest Temperate World Orbiting Quiet Star Discovered

PR Image eso1736a
Artist’s impression of the planet Ross 128 b 

PR Image eso1736b
The sky around the red dwarf star Ross 128

The red dwarf star Ross 128 in the constellation of Virgo



Videos

ESOcast 137 Light: Temperate Planet Orbiting Quiet Red Dwarf (4K UHD)
ESOcast 137 Light: Temperate Planet Orbiting Quiet Red Dwarf (4K UHD)

Zooming in on Ross 128
PR Video eso1736b
Zooming in on Ross 128

Flying through the Ross 128 planetary system
Flying through the Ross 128 planetary system




ESO’s HARPS instrument finds Earth-mass exoplanet around Ross 128


A temperate Earth-sized planet has been discovered only 11 light-years from the Solar System by a team using ESO’s unique planet-hunting HARPS instrument. The new world has the designation Ross 128 b and is now the second-closest temperate planet to be detected after Proxima b. It is also the closest planet to be discovered orbiting an inactive red dwarf star, which may increase the likelihood that this planet could potentially sustain life. Ross 128 b will be a prime target for ESO’s Extremely Large Telescope, which will be able to search for biomarkers in the planet's atmosphere.

A team working with ESO’s High Accuracy Radial velocity Planet Searcher (HARPS) at the La Silla Observatory in Chile has found that the red dwarf star Ross 128 is orbited by a low-mass exoplanet every 9.9 days. This Earth-sized world is expected to be temperate, with a surface temperature that may also be close to that of the Earth. Ross 128 is the “quietest” nearby star to host such a temperate exoplanet.

This discovery is based on more than a decade of HARPS intensive monitoring together with state-of-the-art data reduction and analysis techniques. Only HARPS has demonstrated such a precision and it remains the best planet hunter of its kind, 15 years after it began operations,” explains Nicola Astudillo-Defru (Geneva Observatory – University of Geneva, Switzerland), who co-authored the discovery paper.

Red dwarfs are some of the coolest, faintest — and most common — stars in the Universe. This makes them very good targets in the search for exoplanets and so they are increasingly being studied. In fact, lead author Xavier Bonfils (Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS, Grenoble, France), named their HARPS programme The shortcut to happiness, as it is easier to detect small cool siblings of Earth around these stars, than around stars more similar to the Sun [1].

Many red dwarf stars, including Proxima Centauri, are subject to flares that occasionally bathe their orbiting planets in deadly ultraviolet and X-ray radiation. However, it seems that Ross 128 is a much quieter star, and so its planets may be the closest known comfortable abode for possible life.

Although it is currently 11 light-years from Earth, Ross 128 is moving towards us and is expected to become our nearest stellar neighbour in just 79 000 years — a blink of the eye in cosmic terms. Ross 128 b will by then take the crown from Proxima b and become the closest exoplanet to Earth!

With the data from HARPS, the team found that Ross 128 b orbits 20 times closer than the Earth orbits the Sun. Despite this proximity, Ross 128 b receives only 1.38 times more irradiation than the Earth. As a result, Ross 128 b’s equilibrium temperature is estimated to lie between -60 and 20°C, thanks to the cool and faint nature of its small red dwarf host star, which has just over half the surface temperature of the Sun. While the scientists involved in this discovery consider Ross 128b to be a temperate planet, uncertainty remains as to whether the planet lies inside, outside, or on the cusp of the habitable zone, where liquid water may exist on a planet’s surface [2].

Astronomers are now detecting more and more temperate exoplanets, and the next stage will be to study their atmospheres, composition and chemistry in more detail. Vitally, the detection of biomarkers such as oxygen in the very closest exoplanet atmospheres will be a huge next step, which ESO’s Extremely Large Telescope (ELT) is in prime position to take [3].

New facilities at ESO will first play a critical role in building the census of Earth-mass planets amenable to characterisation. In particular, NIRPS, the infrared arm of HARPS, will boost our efficiency in observing red dwarfs, which emit most of their radiation in the infrared. And then, the ELT will provide the opportunity to observe and characterise a large fraction of these planets,” concludes Xavier Bonfils.



Notes

[1] A planet orbiting close to a low-mass red dwarf star has a larger gravitational effect on the star than a similar planet orbiting further out from a more massive star like the Sun. As a result, this “reflex motion” velocity is much easier to spot. However, the fact that red dwarfs are fainter makes it harder to collect enough signal for the very precise measurements that are needed.

[2] The habitable zone is defined by the range of orbits around a star in which a planet can possess the appropriate temperature for liquid water to exist on the planet’s surface.

[3] This is only possible for the very few exoplanets that are close enough to the Earth to be angularly resolved from their stars.


More Information

This research was presented in a paper entitled “A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs”, by X. Bonfils et al., to appear in the journal Astronomy & Astrophysics.

The team is composed of X. Bonfils (Univ. Grenoble Alpes, CNRS, IPAG, Grenoble, France [IPAG]), N. Astudillo-Defru (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), R. Díaz (CONICET – Universidad de Buenos Aires, Instituto de Astronomía y Física del Espacio (IAFE), Buenos Aires, Argentina), J.-M. Almenara (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), T. Forveille (IPAG), F. Bouchy (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), X. Delfosse (IPAG), C. Lovis (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), M. Mayor (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), F. Murgas (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain), F. Pepe (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), N. C. Santos (Instituto de Astrofísica e Ciências do Espaço and Universidade do Porto, Portugal), D. Ségransan (Observatoire de Genève, Université de Genève, Sauverny, Switzerland), S. Udry (Observatoire de Genève, Université de Genève, Sauverny, Switzerland) and A. Wü̈nsche (IPAG).

ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile and by 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



Contacts

Xavier Bonfils
Institut de Planétologie et d'Astrophysique de Grenoble – Université Grenoble-Alpes/CNRS
Grenoble, France

Nicola Astudillo-Defru
Geneva Observatory – University of Geneva
Geneva, Switzerland

Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591

Source: ESO

Wednesday, November 15, 2017

Hitomi Mission Glimpses Cosmic 'Recipe' for the Nearby Universe

The Perseus galaxy cluster, located about 240 million light-years away, is shown in this composite of visible light (green and red) and near-infrared images from the Sloan Digital Sky Survey. Unseen here is a thin, hot, X-ray-emitting gas that fills the cluster. Credit: Robert Lupton and the Sloan Digital Sky Survey Consortium.  Hi-res image
 
Hitomi's Soft X-ray Spectrometer (SXS) instrument captured data from two overlapping areas of the Perseus galaxy cluster (blue outlines, upper right) in February and March 2016. The resulting spectrum has 30 times the detail of any previously captured, revealing many X-ray peaks associated with chromium, manganese, nickel and iron. Dark blue lines in the insets indicate the actual X-ray data points and their uncertainties.Credits: NASA's Goddard Space Flight Center. Hi-res image
 
Illustration of Hitomi, an X-ray astronomy observatory
Credits: Japan Aerospace Exploration Agency (JAXA).  Hi-res image

The Soft X-ray Spectrometer (SXS) on Hitomi, photographed Nov. 27, 2015, at Tsukuba Space Center in Japan. The SXS permitted scientists to observe the detailed motions and chemical composition of gas permeating the Perseus galaxy cluster. Credits: JAXA.  Hi-res image



Before its brief mission ended unexpectedly in March 2016, Japan's Hitomi X-ray observatory captured exceptional information about the motions of hot gas in the Perseus galaxy cluster. Now, thanks to unprecedented detail provided by an instrument developed jointly by NASA and the Japan Aerospace Exploration Agency (JAXA), scientists have been able to analyze more deeply the chemical make-up of this gas, providing new insights into the stellar explosions that formed most of these elements and cast them into space.

The Perseus cluster, located 240 million light-years away in its namesake constellation, is the brightest galaxy cluster in X-rays and among the most massive near Earth. It contains thousands of galaxies orbiting within a thin hot gas, all bound together by gravity. The gas averages 90 million degrees Fahrenheit (50 million degrees Celsius) and is the source of the cluster's X-ray emission.

Using Hitomi's high-resolution Soft X-ray Spectrometer (SXS) instrument, researchers observed the cluster between Feb. 25 and March 6, 2016, acquiring a total exposure of nearly 3.4 days. The SXS observed an unprecedented spectrum, revealing a landscape of X-ray peaks emitted from various chemical elements with a resolution some 30 times better than previously seen.

In a paper published online in the journal Nature on Nov. 13, the science team shows that the proportions of elements found in the cluster are nearly identical to what astronomers see in the Sun.

"There was no reason to expect that initially," said coauthor Michael Loewenstein, a University of Maryland research scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The Perseus cluster is a different environment with a different history from our Sun's. After all, clusters represent an average chemical distribution from many types of stars in many types of galaxies that formed long before the Sun.

One group of elements is closely tied to a particular class of stellar explosion, called Type Ia supernovas. These blasts are thought to be responsible for producing most of the universe's chromium, manganese, iron and nickel — metals collectively known as "iron-peak" elements.

Type Ia supernovas entail the total destruction of a white dwarf, a compact remnant produced by stars like the Sun. Although stable on its own, a white dwarf can undergo a runaway thermonuclear explosion if it's paired with another object as part of a binary system. This occurs either by merging with a companion white dwarf or, when paired with a nearby normal star, by stealing some of partner's gas. The transferred matter can accumulate on the white dwarf, gradually increasing its mass until it becomes unstable and explodes.

An important open question has been whether the exploding white dwarf is close to this stability limit — about 1.4 solar masses — regardless of its origins. Different masses produce different amounts of iron-peak metals, so a detailed tally of these elements over a large region of space, like the Perseus galaxy cluster, could indicate which kinds of white dwarfs blew up more often.

"It turns out you need a combination of Type Ia supernovas with different masses at the moment of the explosion to produce the chemical abundances we see in the gas at the middle of the Perseus cluster," said Hiroya Yamaguchi, the paper's lead author and a UMD research scientist at Goddard. "We confirm that at least about half of Type Ia supernovas must have reached nearly 1.4 solar masses." 

Taken together, the findings suggest that the same combination of Type Ia supernovas producing iron-peak elements in our solar system also produced these metals in the cluster's gas. This means both the solar system and the Perseus cluster experienced broadly similar chemical evolution, suggesting that the processes forming stars — and the systems that became Type Ia supernovas — were comparable in both locations. 

"Although this is just one example, there’s no reason to doubt that this similarity could extend beyond our Sun and the Perseus cluster to other galaxies with different properties," said coauthor Kyoko Matsushita, a professor of physics at the Tokyo University of Science.  

Although short-lived, the Hitomi mission and its revolutionary SXS instrument —developed and built by Goddard scientists working closely with colleagues from several institutions in the United States, Japan and the Netherlands — have demonstrated the promise of high-resolution X-ray spectrometry. 

"Hitomi has permitted us to delve deeper into the history of one of the largest structures in the universe, the Perseus galaxy cluster, and explore how particles and materials behave in the extreme conditions there," said Goddard's Richard Kelley, the U.S. principal investigator for the Hitomi collaboration. "Our most recent calculations have provided a glimpse into how and why certain chemical elements are distributed throughout galaxies beyond our own."

JAXA and NASA scientists are now working to regain the science capabilities lost in the Hitomi mishap by collaborating on the X-ray Astronomy Recovery Mission (XARM), expected to launch in 2021. One of its instruments will have capabilities similar to the SXS flown on Hitomi.

Hitomi launched on Feb. 17, 2016, and suffered a mission-ending spacecraft anomaly 38 days later. Hitomi, which translates to "pupil of the eye," was known before launch as ASTRO-H. The mission was developed by the Institute of Space and Astronautical Science, a division of JAXA. It was built jointly by an international collaboration led by JAXA, with contributions from Goddard and other institutions in the United States, Japan, Canada and Europe.

For more information about ASTRO-H, visit:  http://www.nasa.gov/astro-h



By Raleigh McElvery and Francis Reddy
NASA's Goddard Space Flight Center, Greenbelt, Md.

Editor: Rob Garner

Source: NASA/Hitomi

Tuesday, November 14, 2017

A gigantic cosmic bubble

 Credit: ESO/T. Contini (IRAP, Toulouse), B. Epinat (LAM, Marseille)


Measuring more than 300 000 light-years across, three times the diameter of the Milky Way, this colourful bubble of ionised gas is the biggest to ever have been discovered. The enormous bubble contains 10 individual galaxies and is situated in a particularly dense region of a galaxy group called COSMOS-Gr30, 6.5 billion light-years away from Earth. Targeted due to its high density of galaxies, this group is extremely varied — some galaxies are actively forming stars while others are passive; some are bright while others are dim; some are massive and others are tiny.

This record-breaking bubble was discovered and studied in detail thanks to the incredible sensitivity of the MUSE instrument, mounted on ESO’s Very Large Telescope. Operating in visible wavelengths, MUSE combines the capabilities of an imaging device with the measuring capacity of a spectrograph, creating a unique and powerful tool that can shed light on cosmological objects that would otherwise remain in the dark.

MUSE’s powerful eye on the sky has allowed astronomers to understand that this large pocket of gas is not pristine, but was expelled from galaxies either during violent interactions or by superwinds driven by active black holes and supernovae. They also studied how this magnificent bubble became ionised. It is believed that the gas in the upper area (shown in blue) was ionised by intense electromagnetic radiation from newborn stars and shock waves stemming from galactic activity. 

Astronomers suspect that the violent red active galactic nucleus towards the lower left of the image could have ripped the electrons from their atoms.

 Links



Source: ESO/Potw

Monday, November 13, 2017

Duo of Titanic Galaxies Captured in Extreme Starbursting Merger

Composite image of ADFS-27 galaxy pair. The background image is from ESA's Herschel Space Observatory. The object was then detected by ESO's Atacama Pathfinder EXperiment (APEX) telescope (middle image). ALMA (right) was able to identify two galaxies: ADFS-27N (for North) and ADFS-27S (for South). The starbursting galaxies are about 12.8 billion light-years from Earth and destined to merge into a single, massive galaxy. Credit: NRAO/AUI/NSF, B. Saxton; ESA Herschel; ESO APEX; ALMA (ESO/NAOJ/NRAO); D. Riechers
Artist impression of two starbursting galaxies beginning to merge in the early universe.
Credit: NRAO/AUI/NSF

Animation zoom-in of the composite image of ADFS-27 galaxy pair. The initial image is from ESA's Herschel Space Observatory. The object was then detected by ESO's Atacama Pathfinder EXperiment (APEX) telescope. ALMA (final zoom) was able to identify two galaxies: ADFS-27N (for North) and ADFS-27S (for South). The starbursting galaxies are about 12.8 billion light-years from Earth and destined to merge into a single, massive galaxy. Credit: ESA/Herschel; ESO/APEX; ALMA (ESO/NAOJ/NRAO); D. Riechers et al. 2017


Pair of Exceptionally Rare Hyper-luminous Galaxies Discovered with ALMA 

New observations with the Atacama Large Millimeter/submillimeter Array (ALMA) have uncovered the never-before-seen close encounter between two astoundingly bright and spectacularly massive galaxies in the early universe. These so-called hyper-luminous starburst galaxies are exceedingly rare at this epoch of cosmic history — near the time when galaxies first formed — and may represent one of the most-extreme examples of violent star formation ever observed.

Astronomers captured these two interacting galaxies, collectively known as ADFS-27, as they began the gradual process of merging into a single, massive elliptical galaxy. An earlier sideswiping encounter between the two helped to trigger their astounding bursts of star formation. Astronomers speculate that this merger may eventually form the core of an entire galaxy cluster. Galaxy clusters are among the most massive structures in the universe.

“Finding just one hyper-luminous starburst galaxy is remarkable in itself. Finding two of these rare galaxies in such close proximity is truly astounding,” said Dominik Riechers, an astronomer at Cornell University in Ithaca, New York, and lead author on a paper appearing in the Astrophysical Journal. “Considering their extreme distance from Earth and the frenetic star-forming activity inside each, it’s possible we may be witnessing the most intense galaxy merger known to date.”

The ADFS-27 galaxy pair is located approximately 12.7 billion light-years from Earth in the direction of the Dorado constellation. At this distance, astronomers are viewing this system as it appeared when the universe was only about one billion years old.

Astronomers first detected this system with the European Space Agency’s Herschel Space Observatory. It appeared as a single red dot in the telescope’s survey of the southern sky. These initial observations suggested that the apparently faint object was in fact both extremely bright and extremely distant. Follow-up observations with the Atacama Pathfinder EXperiment (APEX) telescope confirmed these initial interpretations and paved the way for the more detailed ALMA observations.

With its higher resolution and greater sensitivity, ALMA precisely measured the distance to this object and revealed that it was in fact two distinct galaxies. The pairing of otherwise phenomenally rare galaxies suggests that they reside within a particularly dense region of the universe at that period in its history, the astronomers said.

The new ALMA observations also indicate that the ADFS-27 system has approximately 50 times the amount of star-forming gas as the Milky Way. “Much of this gas will be converted into new stars very quickly,” said Riechers. “Our current observations indicate that these two galaxies are indeed producing stars at a breakneck pace, about one thousand times faster than our home galaxy.”

The galaxies — which would appear as flat, rotating disks — are brimming with extremely bright and massive blue stars. Most of this intense starlight, however, never makes it out of the galaxies themselves; there is simply too much obscuring interstellar dust in each.

This dust absorbs the brilliant starlight, heating up until it glows brightly in infrared light. As this light travels the vast cosmic distances to Earth, the ongoing expansion of the universe shifts the once infrared light into longer millimeter and submillimeter wavelengths, all thanks to the Doppler efecct.

  
Doppler effect,

ALMA was specially designed to detect and study light of this nature, which enabled the astronomers to resolve the source of the light into two distinct objects. The observations also show the basic structures of the galaxies, revealing tail-like features that were spun-off during their initial encounter.
The new observations also indicate that the two galaxies are about 30,000 light-years apart, moving at roughly several hundred kilometers per second relative to each other. As they continue to interact gravitationally, each galaxy will eventually slow and fall toward the other, likely leading to several more close encounters before merging into one massive, elliptical galaxy. The astronomers expect this process to take a few hundred million years.

“Due to their great distance and dustiness, these galaxies remain completely undetected at visible wavelengths,” noted Riechers. “Eventually, we hope to combine the exquisite ALMA data with future infrared observations with NASA’s James Webb Space Telescope. These two telescopes will form an astronomer’s ‘dream team’ to better understand the nature of this and other such exceptionally rare, extreme systems.”

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.



This research is presented in a paper titled “Rise of the titans: a dusty, hyper-luminous ‘870 µm riser’ galaxy at z~6,” by D. Riechers, et al., appearing in the Astrophysical Journal .  [http://iopscience.iop.org/article/10.3847/1538-4357/aa8ccf ].

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.



Friday, November 10, 2017

Cosmic Relics

Credit: ESA/Hubble & NASA


This NASA/ESA Hubble Space Telescope image seems to sink into the screen, plunging the viewer into the dark depths of the early Universe. Massive galaxy clusters — such as the subject of this image, Abell 1300 — help us to better understand the cosmos. They are essentially giant natural telescopes, magnifying the light from any galaxies sitting behind them and helping us peer further back in time.

This bizarre kind of time travel is possible due to a phenomenon called gravitational lensing, whereby the gravitational influence of a massive object such as Abell 1300 acts like a lens, bending the very fabric of space around it and thus causing more distant light to move in a curved path. To the observer, the source of the light — a background object such as a primordial galaxy, for example — appears both distorted and magnified. The lensing power of massive clusters has helped us to discover some of the most distant known galaxies in the Universe. Hubble has observed this phenomenon many times; see a selection of images here.

This image was taken by Hubble’s Advanced Camera for Surveys and Wide-Field Camera 3 as part of an observing program called RELICS. The program imaged 41 massive galaxy clusters over the course of 390 Hubble orbits and 100 Spitzer Space Telescope observing hours, aiming to find the brightest distant galaxies. Studying these galaxies in more detail with both current telescopes and the future NASA/ESA/CSA James Webb Space Telescope (JWST) will hopefully tell us more about our cosmic origins.



Thursday, November 09, 2017

Hubble Movie Shows Movement of Light Echo Around Exploded Star

Light Echo around SN 2014J in M82  
Credits: NASA, ESA, and Y. Yang (Texas A&M University and Weizmann Institute of Science, Israel)
Acknowledgment: M. Mountain (AURA) and The Hubble Heritage Team (STScI/AURA)


Voices reverberating off mountains and the sound of footsteps bouncing off walls are examples of an echo. Echoes happen when sound waves ricochet off surfaces and return to the listener. 

Space has its own version of an echo. It’s not made with sound but with light, and occurs when light bounces off dust clouds. 

The Hubble telescope has just captured one of these cosmic echoes, called a “light echo,” in the nearby starburst galaxy M82, located 11.4 million light-years away. A movie assembled from more than two years’ worth of Hubble images reveals an expanding shell of light from a supernova explosion sweeping through interstellar space three years after the stellar blast was discovered. The “echoing” light looks like a ripple expanding on a pond. The supernova, called SN 2014J, was discovered on Jan. 21, 2014.

A light echo occurs because light from the stellar blast travels different distances to arrive at Earth. Some light comes to Earth directly from the supernova blast. Other light is delayed because it travels indirectly. In this case, the light is bouncing off a huge dust cloud that extends 300 to 1,600 light-years around the supernova and is being reflected toward Earth.
So far, astronomers have spotted only 15 light echoes around supernovae outside our Milky Way galaxy. Light echo detections from supernovae are rarely seen because they must be nearby for a telescope to resolve them.


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Donna Weaver / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
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Yi Yang
Weizmann Institute of Science, Rehovot, Israel
972-8-934-6505

yi.yang@weizmann.ac.il


Shocking Results of Galaxy-Cluster Collisions

Composite image of Abell 2744 region, with radio, X-Ray, and optical (visible light) data combined. Credit: Pearce et al.; Bill Saxton, NRAO/AUI/NSF; Chandra, Subaru; ESO. Hi-res image

Radio-only image of Abell 2744 region, showing radio-emitting features caused by subatomic particles accelerated to high speeds by the collisions of giant clusters of galaxies.  Credit: Pearce et al., NRAO/AUI/NS. Hi-res image

Animated GIF cycles through the individual images (radio, X-ray, optical) of Abell 2744. 
Credit: Pearce et al.; Bill Saxton, NRAO/AUI/NSF; Chandra; Subaru; ESO. Hi-res image


A giant collision of several galaxy clusters, each containing hundreds of galaxies, has produced this spectacular panorama of shocks and energy. The collisions generated shock waves that set off a celestial fireworks display of bright radio emission, seen as red and orange. In the center of the image, the purple indicates X-rays caused by extreme heating.

The region is collectively known as Abell 2744, some 4 billion light-years from Earth. The radio portion of the image comes from new observations made with the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), and is combined with earlier data from NASA’s Chandra X-ray observatory. Both are overlaid on an image at visible-light wavelengths made with data from the Subaru telescope and the Very Large Telescope (VLT). The new VLA observations revealed previously undetected regions where shocks accelerated subatomic particles, causing radio emission.

Astronomers are studying the combined image in an attempt to decipher the sequence of galaxy-cluster collisions. Currently, they said, evidence indicates a North-South (top-bottom in the image) collision of subclusters and an East-West (left-right in the image) collision. There is a possible third collision, and the astronomers continue to analyze their data to uncover more details about the region’s complex history of collisions and their aftermath.

The scientists reported their findings in a paper in the Astrophysical Journal by Connor Pearce, of the Harvard-Smithsonian Center for Astrophysics and the University of Southampton in the UK, and an international team of colleagues.

The National Radio Astronomy Obser vatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

 
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Wednesday, November 08, 2017

The Dynamic Duo: Jupiter's Independently Pulsating X-ray Auroras

Jupiter's Aurora
Credit X-ray: NASA/CXC/UCL/W.Dunn et al, Optical: South Pole: NASA/JPL-Caltech/SwRI/MSSS/Gerald Eichstädt /Seán Doran; North Pole: NASA/JPL-Caltech/SwRI/MSSS


Jupiter's intense northern and southern lights, or auroras, behave independently of each other according to a new study using NASA's Chandra X-ray and ESA's XMM-Newton observatories.

Using XMM-Newton and Chandra X-ray observations from March 2007 and May and June 2016, a team of researchers produced maps of Jupiter's X-ray emissions and identified an X-ray hot spot at each pole. Each hot spot can cover an area equal to about half the surface of the Earth.

The team found that the hot spots had very different characteristics. The X-ray emission at Jupiter's south pole consistently pulsed every 11 minutes, but the X-rays seen from the north pole were erratic, increasing and decreasing in brightness — seemingly independent of the emission from the south pole.

This makes Jupiter particularly puzzling. X-ray auroras have never been detected from our Solar System's other gas giants, including Saturn. Jupiter is also unlike Earth, where the auroras on our planet's north and south poles generally mirror each other because the magnetic fields are similar.

To understand how Jupiter produces its X-ray auroras, the team of researchers plans to combine new and upcoming X-ray data from Chandra and XMM-Newton with information from NASA's Juno mission, which is currently in orbit around the planet. If scientists can connect the X-ray activity with physical changes observed simultaneously with Juno, they may be able to determine the process that generates the Jovian auroras and by association X-ray auroras at other planets.

Illustration of Jupiter
Credit: NASA/CXC/M.Weiss


One theory that the X-ray and Juno observations may help to prove or disprove is that Jupiter's X-ray auroras are caused by interactions at the boundary between Jupiter's magnetic field, which is generated by electrical currents in the planet's interior, and the solar wind, a high-speed flow of particles streaming from the Sun. The interactions between the solar wind and Jupiter's magnetic field can cause the latter to vibrate and produce magnetic waves. Charged particles can surf these waves and gain energy. Collisions of these particles with Jupiter's atmosphere produce the bright flashes of X-rays observed by Chandra and XMM. Within this theory the 11-minute interval would represent the time for a wave to travel along one of Jupiter's magnetic field lines. 

The difference in behavior between the Jovian north and south poles may be caused by the difference in visibility of the two poles. Because the magnetic field of Jupiter is tilted, we are able to see much more of the northern aurora than the southern aurora. Therefore for the north pole we may be able to observe regions where the magnetic field connects to more than one location, with several different travel times, while for the south pole we can only observe regions where the magnetic field connects to one location. This would cause the behavior of the north pole to appear erratic compared to the south pole.

A larger question is how does Jupiter give the particles in its magnetosphere (the realm controlled by Jupiter's magnetic field) the huge energies needed to make X-rays? Some of the X-ray emission observed with Chandra can only be produced if Jupiter accelerates oxygen ions to such high energies that when they violently collide with the atmosphere all eight of their electrons are torn off. Scientists hope to determine what impact these particles, which crash into the planet's poles at thousands of kilometers per second, have on the planet itself. Do these high-energy particles affect the Jovian weather and the chemical composition of its atmosphere? Can they explain the anomalously high temperatures found in certain places in Jupiter's atmosphere? These are the questions that Chandra, XMM-Newton, and Juno may be able to help answer in the future.

A paper describing these results appeared in the October 30th issue of Nature Astronomy, led by William Dunn of the University College London. NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.




 Fast Facts for Jupiter:

Scale: This image is about 37 arcsec across (139,822 km = Jupiter's diameter) as viewed from Earth
Category: Solar System
Observation Date: May 24 & Jun 01, 2016
Observation Time: 22 hours
Obs. ID: 18608 & 18609
Instrument: HRC
References: Dunn, W.R. et al, 2017, Nature Astronomy, 1, 758
Color Code: X-ray (purple), optical (pseudocolor)
Distance Estimate: About 793 million km (on date of Chandra observations)



Tuesday, November 07, 2017

MACS J1149.5+2233: A Fusion of Galaxy Clusters

MACS J1149.5+2233
Credit X-ray: NASA/CXC/SAO; Optical: NASA/STScI; Radio: NSF/NRAO/AUI/VLA



A Tour of Abell 3411



MACS J1149.5+2233 (MACS J1149 for short) is a system of merging galaxy clusters located about 5 billion light years from Earth. This galaxy cluster was one of six that have been studied as part of the "Frontier Fields" project. This research effort included long observations of galaxy clusters with powerful telescopes that detected different types of light, including NASA's Chandra X-ray Observatory.

Astronomers are using the Frontier Fields data to learn more about how galaxy clusters grow via collisions. Galaxy clusters are enormous collections of hundreds or even thousands of galaxies and vast reservoirs of hot gas embedded in massive clouds of dark matter, invisible material that does not emit or absorb light but can be detected through its gravitational effects.

This new image of MACS J1149 combines X-rays from Chandra (diffuse blue), optical data from Hubble (red, green, blue), and radio emission from the Very Large Array (pink). The image is about four million light years across at the distance of MACS J1149.

The Chandra data reveal gas in the merging clusters with temperatures of millions of degrees. The optical data show galaxies in the clusters and other, more distant, galaxies lying behind the clusters. Some of these background galaxies are highly distorted because of gravitational lensing, the bending of light by massive objects. This effect can also magnify the light from these objects, enabling astronomers to study background galaxies that would otherwise be too faint to detect. Finally, the structures in the radio data trace enormous shock waves and turbulence. The shocks are similar to sonic booms, and are generated by the mergers of smaller clusters of galaxies.

NASA's Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, controls Chandra's science and flight operations.



Fast Facts for MACS J1149.5+2233:

Scale: Image is 3.2 arcmin across (about 4.7 million light years)
Category: Groups & Clusters of Galaxies
Coordinates (J2000): RA 11h 49m 36.3s | Dec 22° 23´ 58.1"
Constellation: Leo
Observation Date: 8 pointings between Jun 2001 and Feb 2015
Observation Time: 101 hours 30 min (4 days 5 hours 30 min)
Obs. ID: 1656, 3589, 16238, 16239, 16306, 16582, 17595, 17596
Instrument: ACIS
Color Code: X-ray (Blue); Optical (Red, Green, Blue); Radio (Pink)
Distance Estimate: About 5 billion light years


Monday, November 06, 2017

Gemini Observatory Confirms Spiral Nature of Extremely Distant Lensed Galaxy

The massive galaxy cluster bends the light of the most ancient spiral galaxy behind it, producing two highly magnified images that allow astronomers to study the spiral structures in great details. Image credit: James Josephides. Full resolution JPEG


Gemini Observatory, using the Near-Infrared Integral Field Spectrograph on the Gemini North telescope in Hawai‘i, has confirmed the spiral nature of what is now the most distant known spiral galaxy. The galaxy's light, revealing how the galaxy looked some 11 billion years ago, is gravitationally lensed by a massive foreground cluster of galaxies to help reveal the distant pinwheel nature of the galaxy.

The following is a press release from Swinburne University of Technology in Australia.

The most ancient spiral galaxy discovered to date is revealing its secrets to a team of astronomers at Swinburne University of Technology and the Australian National University (ANU), both part of the Australian Research Council Centre of Excellence in All Sky Astrophysics in 3D (ASTRO 3D). The galaxy, known as A1689B11, existed 11 billion years in the past, just 2.6 billion years after the Big Bang, when the Universe was only one fifth of its present age. It is thus the most ancient spiral galaxy discovered so far.

The researchers used a powerful technique that combines gravitational lensing with the cutting-edge instrument, the Near-infrared Integral Field Spectrograph (NIFS) on the Gemini North telescope in Hawai‘i, to verify the vintage and spiral nature of this galaxy. NIFS is Australia’s first Gemini instrument that was designed and built by the late Peter McGregor at the ANU.

Gravitational lenses are Nature’s largest telescopes, created by massive clusters composed of thousands of galaxies and dark matter. The cluster bends and magnifies the light of galaxies behind it in a manner similar to an ordinary lens, but on a much larger scale. “This technique allows us to study ancient galaxies in high resolution with unprecedented detail,” says Swinburne astronomer Dr Tiantian Yuan, who led the research team.

“We are able to look 11 billion years back in time and directly witness the formation of the first, primitive spiral arms of a galaxy.” Co-author, Princeton University’s Dr Renyue Cen, says: “Studying ancient spirals like A1689B11 is a key to unlocking the mystery of how and when the Hubble sequence emerges.”

“Spiral galaxies are exceptionally rare in the early Universe, and this discovery opens the door to investigating how galaxies transition from highly chaotic, turbulent discs to tranquil, thin discs like those of our own Milky Way galaxy.”

Dr Yuan says the study shows some surprising features of A1689B11.

“This galaxy is forming stars 20 times faster than galaxies today – as fast as other young galaxies of similar masses in the early Universe. However, unlike other galaxies of the same epoch, A1689B11 has a very cool and thin disc, rotating calmly with surprisingly little turbulence. This type of spiral galaxy has never been seen before at this early epoch of the Universe!”

This research is an international collaboration including astrophysicists from the University of Lyon in France, Princeton University in the USA and Hebrew University in Israel. It has been accepted for publication in The Astrophysical Journal. A preprint version is available here.


Science Contacts:

Tiantian Yuan
Swinburne University of Technology
Email: tiantianyuan@swin.edu.au
Desk: +613 9214 5948
Cell: +61 404 029 550


Media Contacts:

Lea Kivivali
Swinburne University of Technology
Email: lkivivali@swin.edu.au
Desk: +613 9214 5428
Cell: +61 410 569 311

Peter Michaud
Public Information and Outreach Manager
Gemini Observatory
Hilo, Hawai‘i
Email: pmichaud@gemini.edu
Desk: 808 974-2510
Cell: 808 936-6643


Sunday, November 05, 2017

Minor Merger Kicks Supermassive Black Hole into High Gear

Figure 1:  The deep image of Messier 77 taken with the Hyper Suprime-Cam (HSC) mounted at the Subaru Telescope. The picture is created by adding the color information from the Sloan Digital Sky Survey (Note 1) to the monochromatic image acquired by the HSC. (Credit: NAOJ/SDSS/David Hogg/Michael Blanton. Image Processing: Ichi Tanaka)

The galaxy Messier 77 (M77) is famous for its super-active nucleus that releases enormous energy across the electromagnetic spectrum, ranging from x-ray to radio wavelengths. Yet, despite its highly active core, the galaxy looks like any normal quiet spiral. There's no visual sign of what is causing its central region to radiate so extensively. It has long been a mystery why only the center of M77 is so active. Astronomers suspect a long-ago event involving a sinking black hole, which could have kicked the core into high gear.

To test their ideas about why the central region of M77 beams massive amounts of radiation, a team of researchers at the National Astronomical Observatory of Japan and the Open University of Japan used the Subaru Telescope to study M77. The unprecedented deep image of the galaxy reveals evidence of a hidden minor merger billions of years ago. The discovery gives crucial evidence for the minor merger origin of active galactic nuclei.

The Mystery of Seyfert Galaxies

The galaxy Messier 77 (NGC 1068) is famous for harboring an active nucleus at its core that releases an enormous amount of energy. The existence of such active galaxies in the nearby universe was first noted by the American astronomer Carl Seyfert more than 70 years ago. Nowadays they are called the Seyfert galaxies (Note 2). Astronomers think that the source of such powerful activity is the gravitational energy released from superheated matter falling onto a supermassive black hole (SMBH) that resides in the center of the host galaxy. The estimated mass of such a SMBH for M77 is about 10 million times that of the Sun.

It takes a massive amount of gas dumped on the galaxy's central black hole to create such strong energies. That may sound like an easy task, but it's actually very difficult. The gas in the galactic disk will circulate faster and faster as it spirals into the vicinity of the SMBH. Then, at some point the "centrifugal force" balances with the gravitational pull of the SMBH. That actually prevents the gas from falling into the center. The situation is similar to water draining out of a bathtub. Due to the centrifugal force, the rapidly rotating water will not drain out rapidly. So, how can the angular momentum be removed from the gas circling near an active galactic nucleus? Finding the answer to that question is one of the big challenges for researchers today.

A Prediction Posed 18 Years Ago

In 1999, Professor Yoshiaki Taniguchi (currently at the Open University of Japan), the team leader of the current Subaru study, published a paper about the driving mechanism of the active nucleus of Seyfert galaxies such as M 77. He pointed out that a past event – a "minor merger" where the host galaxy ate up its "satellite" galaxy (a small low-mass galaxy orbiting it) – would be the key to activating the Seyfert nucleus (Note 3).

Usually, a minor merger event simply breaks up a low-mass satellite galaxy. The resulting debris is absorbed into the disk of the more massive host galaxy before it approaches the center. Therefore, it was not considered as the main driver of the nuclear activity. "However, the situation could be totally different if the satellite galaxy has a (smaller) SMBH in its center (Note 4)," Professor Taniguchi suggests, "because the black hole can never be broken apart. If it exists, it should eventually sink into the center of the host galaxy."

The sinking SMBH from the satellite galaxy would eventually create a disturbance in the rotating gas disk around the main galaxy's SMBH. Then, the disturbed gas would eventually rush into the central SMBH while releasing enormous gravitational energy. "This must be the main ignition mechanism of the active Seyfert nuclei," Taniguchi argued. "The idea can naturally explain the mystery about the morphology of the Seyfert galaxies," said Professor Taniguchi, pointing out the advantage of the model of normal-looking galaxies also being very active at their cores. (Note 5).

Probing the Theory Using the Subaru Telescope

Recent advances in observational technique allow the detection of the extremely faint structure around galaxies, such as loops or debris that are likely made by dynamical interactions with satellite galaxies.. The outermost parts of galaxies are often considered as relatively "quiet" with a longer dynamical timescale than anywhere inside. Simulations show that the faint signature of a past minor merger can remain several billion years after the event. "Such a signature can be a key test for our minor merger hypothesis for Seyfert galaxies. Now it is time to revisit M77," said Taniguchi.

The team's choice to look for 'the past case' was, of course, the Subaru Telescope and its powerful imaging camera, Hyper Suprime-Cam. The observing proposal was accepted and executed on Christmas night 2016. "The data was just amazing," said Dr. Ichi Tanaka, the primary investigator of the project. "Luckily, we could also retrieve the other data that was taken in the past and just released from the Subaru Telescope's data archive. Thus, the combined data we got finally is unprecedentedly deep."

Figure 2: (Left) The newly-discovered, extremely diffuse structures around M77. The innermost color part of the picture shows the bright part of the galaxy (from SDSS: see the center of Figure 1). The middle part in red-brown is the contrast-enhanced expression of the faint one-arm structure (labeled as "Banana") to the right, as well as the ripple structure (labeled as "Ripple") to the left. All the fore/background objects unrelated to M77 are removed during the process. The outermost monochrome part shows the faint ultra-diffuse structures in yellow circles (labelled as "UDO-SE", "UDO-NE", "UDO-SW"). A deep look at them indicates the latter two ("UDO-NE", "UDO-SW") constitute a part of the large loop-like structure. (Credit: NAOJ)

(Right) Artist's impression of M77. The illustration in the right is created and copyrighted by Mr. Akihiro Ikeshita. (Credit: Akihiro Ikeshita

Subaru's great photon-collecting power and the superb performance of the Hyper Suprime-Cam were crucial in the discovery of the extremely faint structures in M77. Their discovery reveals the normal-looking galaxy's hidden violent past.. "Though people may sometimes make a lie, galaxies never do. The important thing is to listen to their small voices to understand the galaxies," said Professor Taniguchi.

The team will expand its study to more Seyfert galaxies using the Subaru Telescope. Dr. Masafumi Yagi, who leads the next phase of the project said, "We will discover more and more evidences of the satellite merger around Seyfert host galaxies. We expect that the project can provide a critical piece for the unified picture for the triggering mechanism for active galactic nuclei."

The result is going to be published in the Volume 69 Issue 6 of the Publications of the Astronomical Society of Japan (I. Tanaka, M.Yagi & Y. Taniguchi 2017, "Morphological evidence for a past minor merger in the Seyfert galaxy NGC 1068"). The research is financially supported by the Basic Research A grant JP16H02166 by the Grant-in-Aid for Scientific Research progrram.



Notes

Note1: The color image by the Sloan Digital Sky Survey used for Figure 1 is under the copyright of David W. Hogg and Michael R. Blanton.

Note 2: Seyfert galaxies are actually a subclass of the active galactic nuclei. There are even more powerful active galactic nuclei called quasar in the universe. Usually quasars are found much farther away than M77.

Note 3: Satellite galaxies are common for large galaxies. For example, there are two bright satellite galaxies called Large and Small Magellanic Clouds associated with our Milky Way. The Andromeda galaxy, our nearest neighbor, also has two bright satellites called Messier 32 and NGC 205.

Note 4: Astronomers believe that most galaxies have an SMBH in their central regions, with its mass mysteriously scaled to the mass of the host galaxy. It is also known that some satellite galaxies also have smaller SMBH. For example, Messier 32 (satellite of the Andromeda galaxy) is likely to have a SMBH much heavier than a million times the mass of our Sun. It is however not easy to directly prove the existence of the SMBH for satellite galaxies due to its light weight.
Note 5: Y. Taniguchi 1999, ApJ, 524, 65, for the reference.

The research team:

  • Ichi Tanaka: Subaru Telescope, National Astronomical Observatory of Japan
  • Masafumi Yagi: National Astronomical Observatory of Japan
  • Yoshiaki Taniguchi: The Open University of Japan