Mysterious “Superbubble” Hollows Out Nebula in New Hubble Image (Cosmology)

N44 is a complex nebula filled with glowing hydrogen gas, dark lanes of dust, massive stars, and many populations of stars of different ages. One of its most distinctive features, however, is the dark, starry gap called a “superbubble,” visible in this Hubble Space Telescope image in the upper central region.

The hole is about 250 light-years wide and its presence is still something of a mystery. Stellar winds expelled by massive stars in the bubble’s interior may have driven away the gas, but this is inconsistent with measured wind velocities in the bubble. Another possibility, since the nebula is filled with massive stars that would expire in titanic explosions, is that the expanding shells of old supernovae sculpted the cosmic cavern.

Astronomers have found one supernova remnant in the vicinity of the superbubble and identified an approximately 5 million year difference in age between stars within and at the rim of the superbubble, indicating multiple, chain-reaction star-forming events. The deep blue area at about 5 o’clock around the superbubble is one of the hottest regions of the nebula and the area of the most intense star formation.

N44 is an emission nebula, which means its gas has been energized, or ionized, by the radiation of nearby stars. As the ionized gas begins to cool from its higher-energy state to a lower-energy state, it emits energy in the form of light, causing the nebula to glow. Located in the Large Magellanic Cloud, N44 spans about 1,000 light-years and is about 170,000 light-years away from Earth.

To zoom in to even more detail, download a full-sized, high-resolution, 288-megapixel image of this large mosaic created through multiple Hubble observations. Download the 153 MB TIF image here: https://svs.gsfc.nasa.gov/14018.

Image credit: NASA, ESA, V. Ksoll and D. Gouliermis (Universität Heidelberg), et al.; Processing: Gladys Kober (NASA/Catholic University of America)


Provided by NASA

Lack Of Massive Black Holes in Telescope Data is Caused by Bias (Astronomy)

Our telescopes have never detected a black hole more massive than twenty times the mass of the Sun. Nevertheless, we now know of their existence as dozens of those black holes have recently been “heard” to merge via gravitational wave radiation. A team of astronomers led by Peter Jonker (SRON/Radboud) has now discovered that these seemingly disparate results can be explained by biases against massive black holes in conventional telescope observations.

In 2015 the LIGO facilities detected gravitational waves for the first time. They were emitted by two massive black holes of several tens the mass of the Sun in the process of merging. This discovery shook the Universe, and also the astronomical community, because few astronomers had predicted that such massive black holes would exist, let alone that they could merge. Before the gravitational wave detections, our conventional telescopes had found proof for the existence of stellar mass black holes in about 20 cases. However, none had ever been found that were as massive as those now observed through gravitational wave radiation emitted during merger. By now about 50 of such merging black hole pairs have been detected, including by the European Virgo detector, again in most cases involving massive black holes. Telescopes still have not found such black holes.

This disparity can be partially explained by the larger volume of the Universe that is being probed by the gravitational wave detectors. LIGO-Virgo can find such more massive black holes more easily because their waves are stronger relative to those from lighter black holes, implying that these could be rare, but loud events. But zero detections of such black holes using telescopes? Black holes, or at least their close environment, lights up when they slowly devour a companion star. Through measurements of the orbital motion of the hapless star, the mass of the black hole can be determined.

A team of astronomers led by Peter Jonker (Radboud University/SRON) realized that telescope observations are biased against detecting massive black holes. Such massive black holes can, in principle, be observed if they eat mass from a companion star. However, the circumstances for those observations have been too difficult in practice, explaining the lack of detections of massive black holes through telescope observations. The largest black holes are formed through imploding massive stars, instead of exploding massive stars (“supernova”). Formed through an implosion, these massive black holes stay put in the same place where their predecessor (the massive star) was born, the plane of the Milky Way galaxy. However, that means that they remain shrouded in dust and gas. Their lighter black hole sisters and brothers, born out of massive stars through supernova explosions, experience a kick ejecting them out of the plane of the Milky Way, making them more readily observable for our telescopes measuring their mass.

Aggravating this bias, as realized by Jonker and colleagues, is that any companion star of a massive black hole must orbit at a relatively large distance, making it rarer for a companion star to be devoured in an observable frenzy. Such episodes are what gives away the existence and location of black holes. Thus, the more massive black holes will more rarely give away their location.

The imminent launch of the James Webb space telescope (JWST) on December 18 will allow astronomers to test these ideas. JWST will for the first time allow the measurement of the mass of several systems of candidate black holes in the plane of the Milky Way. JWST will be sensitive to infrared light, and such light is much less affected by dust and gas than is the optical light typically used by ground-based telescopes. Furthermore, the large size of JWST, and its advantageous position in space, allows JWST to pick out the right star to study among the millions of stars in the plane of the Milky Way. Finally, being above the Earth’s atmosphere, JWST will not be hindered by the infrared light emitted by the atmosphere.

Caption header image: Measurements using electromagnetic (EM) radiation only revealed stellar black holes less massive than about 20 solar masses (purple circles). These black holes all have a companion star that is losing mass to the black hole. This gas stream reveals the existence of the black hole and detailed study of the motion of the companion allows for the mass of the black hole to be measured. LIGO/Virgo measurements of gravitational wave radiation emitted when two black holes merge have allowed the masses of several tens of black holes to be measured since 2015 (blue circles). These black holes are generally more massive than those found through EM radiation. We know now that the lack of massive black holes studied through EM techniques can be caused by a bias against finding and studying the massive black holes. Incidentally, the LIGO/Virgo measurements favor the detection of massive black holes because the signal of their mergers is louder and thus can be detected from systems further out in the Universe compared with the signal of merging lower mass black holes. Nevertheless, LIGO/Virgo is also detecting lower-mass merging black holes. In the near- future the JWST telescope will enable to remove the EM bias. Due to its sensitivity astronomers will be able to measure the mass of black hole candidate systems located at places where the most massive black holes are thought to reside.

Publicatie

Peter G. Jonker, Karamveer Kaur, Nicholas Stone, and Manuel A. P. Torres, ‘The observed mass distribution of Galactic black hole LMXBs is biased against massive black holes’, The Astrophysical Journal


Provided by SRON

Simultaneous Readout of 60 Bolometers For Far-infrared Space Telescopes (Astronomy)

TES bolometers with simultaneous readout of multiple pixels are the candidate detector technology for a number of space missions for sub-millimeter and far-infrared wavelengths, such as LiteBIRD and OST. Qian Wang, a PhD student at SRON and RUG, has demonstrated a simultaneous readout of 60 TES bolometers. Publication in Applied Physics Letters.

Light with sub-millimeter and far-infrared wavelengths from deep space can travel long distances, penetrating right through dust clouds, and brings us information about the history of the universe and the origin of galaxies, stars and planets. However, the long journey has weakened these signals. So we require sensitive detectors operating at a millikelvin temperatures on a space instrument.

Transition edge sensor (TES) bolometers are superconducting detectors taking advantage of the collapse of the superconducting state and therefore a steep increase in the resistance when its temperature even slightly increases. So, their resistance is extremely sensitive to a change of the temperature, caused by the heating power from light. When heated by incoming photons, the tiny change of the temperature can produce measurable current responses in the detector.

Challenges of TES technology used in space missions are not only the sensitivity, but also reading out multiple pixels at the same time. Without this so-called multiplexing—combining the signals from many pixels into a single paired wire—their connecting wires for each pixel would generate too much heat, making it impossible to keep the detectors at the necessary temperature close to absolute zero.

Qian Wang, working closely with Pourya Khosropanah and other members of the SAFARI-FDM team at SRON, led by Gert de Lange, has demonstrated a frequency division multiplexing (FDM) system that can read out 60 TES bolometers simultaneously using only a single paired wire and an amplifier.  The readout noise is lower compared to previous work reported at SRON and by other laboratories, down to a Noise Equipment Power of 0.45 aW/ÖHz. The sensitivities measured in the multiplexing working mode are the same as in a single pixel mode. The researchers expect to read out at least 130 pixels simultaneously if they extend the frequency range used for the current FDM setup. The result demonstrates that the readout technology meets the requirements of the Japanese LiteBIRD space mission and that FDM technology is an option for NASA’s OST mission in the long-term.

Caption header image: Part of a TES bolometer array. Each pixel consists of a TES thermometer and thin tantalum absorber.

Publication

Q. Wang, P. Khosropanah, J. van der Kuur, G. de Lange, M. D. Audley, A. Aminaei, M. L. Ridder, A. J. van der Linden, M. P. Bruijn, F. van der Tak, and J. R. Gao, Frequency division multiplexing readout of 60 low-noise transition-edge sensor bolometers, Appl. Phys. Lett. 119, 182602 (2021); https://doi.org/10.1063/5.0065570


Provided by SRON Netherlands Institute for Space Research

World’s Most Powerful Telescope Keeps Eyes On The Skies (Astronomy)

Australian astronomers hunting for Earth-like planets outside our solar system and investigating the dramatic life and death of stars have been given a major boost.

The newly released 2020 United States Decadal Survey on Astronomy and Astrophysics has listed the revolutionary Giant Magellan Telescope (GMT) as one of its top priorities. The recommendation opens the door for major funding for the construction of the telescope.

The GMT, being built by an international team including researchers from The Australian National University (ANU), is one of the most exciting projects in the world of astronomy.

Sited in the high, dry Atacama desert in Chile, one of the best places on the planet for exploring the Universe, the GMT represents a new generation in ground-based extremely large telescopes. The telescope will use seven of the world’s largest mirrors and the most advanced optics technology to see billions of light years away.

ANU is a major partner in the GMT project and researchers from the University are involved in the design of the telescope’s adaptive optics system, which removes atmospheric blur and gives GMT the sharpest possible images.

Professor Matthew Colless from ANU, a long-time member of the international GMT team, said Australian researchers were a playing a major role “in making the GMT’s unrivalled vision a reality”.

“ANU scientists are designing and building an integral-field spectrograph for the GMT. This will allow scientists to take images and measure spectra so we can better understand supermassive black holes, the birth and evolution of galaxies, and search for planets outside our solar system,” Professor Colless said.

“ANU researchers are also working with fellow Australian scientists to design and build an optical fibre system that will give GMT the widest field of view of any of the giant new telescopes.

“All of this is a major benefit to Australian research and researchers, and will ensure we remain a global leader when it comes to astronomy and astrophysics.”

Mark McAuley, Chief Executive Officer of Astronomy Australia Limited (AAL), said the US announcement would deliver major benefits for Australian researchers.

“This is another example of Australia playing an active role in a major international research project,” he said.

“Our scientists and engineers will continue to design and construct significant components of this incredible telescope, and Australian astronomers will be among the first in line to access the Giant Magellan Telescope and all its possibilities.”

ANU Vice-Chancellor, Professor Brian Schmidt, who won the 2011 Nobel Prize in physics for his work on the expanding Universe, welcomed the US announcement and congratulated the Giant Magellan Telescope consortium.

“My own work on the expanding Universe will benefit significantly from the power of the GMT,” Professor Schmidt said. “The GMT is an incredible innovation; it could one day be the basis of work that leads to another Nobel Prize.

“It’s really encouraging to see the US astronomy community recommending the GMT for major funding by the US Government. It will take the construction of the GMT to the next level and help us unlock a Universe’s worth of discovery.”

ANU and AAL are equal partners in the Giant Magellan Telescope project.

Astronomy Australia Limited (AAL) is a non-profit organisation, whose members are Australian universities and research organisations with a significant astronomical research capability.

About the Giant Magellan Telescope 
The Giant Magellan Telescope is the work of the GMTO Corporation, an international nonprofit organisation headquartered in Pasadena, California. The consortium’s mission is to design, build, and operate the Giant Magellan Telescope to enable cutting-edge scientific observations that will revolutionise humanity’s fundamental understanding of the Universe.

Featured image: The Giant Magellan Telescope © GMTO Corporation


Provided by ANU

Scientists Detect A “Tsunami” of Gravitational Waves (Astronomy)

A team of international scientists, including researchers from The Australian National University (ANU), have unveiled the largest number of gravitational waves ever detected.

The discoveries will help solve some of the most complex mysteries of the Universe, including the building blocks of matter and the workings of space and time.

The global team’s study, published today on ArXiv, made 35 new detections of gravitational waves caused by pairs of black holes merging or neutron stars and black holes smashing together, using the LIGO and Virgo observatories between November 2019 and March 2020.

This brings the total number of detections to 90 after three observing runs between 2015 and 2020.

The new detections are from massive cosmic events, most of them billions of light years away, which hurl ripples through space-time. They include 32 black hole pairs merging, and likely three collisions between neutron stars and black holes.

ANU is one of the key players in the international team making the observations and developing the sophisticated technology to hunt down elusive gravitational waves across the vast expanse of the Universe. 

Distinguished Professor Susan Scott, from the ANU Centre for Gravitational Astrophysics, said the latest discoveries represented “a tsunami” and were a “major leap forward in our quest to unlock the secrets of the Universe’s evolution”.

“These discoveries represent a tenfold increase in the number of gravitational waves detected by LIGO and Virgo since they started observing,” Distinguished Professor Scott said.  

“We’ve detected 35 events. That’s massive! In contrast, we made three detections in our first observing run, which lasted four months in 2015-16.

“This really is a new era for gravitational wave detections and the growing population of discoveries is revealing so much information about the life and death of stars throughout the Universe.

“Looking at the masses and spins of the black holes in these binary systems indicates how these systems got together in the first place.

“It also raises some really fascinating questions. For example, did the system originally form with two stars that went through their life cycles together and eventually became black holes? Or were the two black holes thrust together in a very dense dynamical environment such as at the centre of a galaxy?”

Distinguished Professor Scott, who is also a Chief Investigator of the ARC Centre of Excellence for Gravitational Wave Discovery (OzGrav), said the continual improvement of gravitational wave detector sensitivity was helping drive an increase in detections.

“This new technology is allowing us to observe more gravitational waves than ever before,” she said.

“We are also probing the two black hole mass gap regions and providing more tests of Einstein’s theory of general relativity.

“The other really exciting thing about the constant improvement of the sensitivity of the gravitational wave detectors is that this will then bring into play a whole new range of sources of gravitational waves, some of which will be unexpected.”

Featured image: Two black holes merge to become one © NASA


Provided by Australian National University