Discovering Magnetized Inflow Accreting to the center of Milky Way Galaxy – An important force to transport gas to the supermassive black hole Sagittarius A*

Is magnetic field an important guiding force for gas accreting to supermassive black hole (SMBH) — for example, the one that our Milky Way Galaxy hosts? The role of magnetic field in this subject is little understood and trying to observe it has been challenging to astronomers. Researchers at the Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), Taiwan, led by Dr. Pei-Ying Hsieh, have utilized a measurement of high resolution data by using the instruments on the James Clerk Maxwell Telescope (JCMT). Their result provides clear evidences in showing that the orientation of the magnetic field is in alignment with the molecular torus and ionized streamers rotating with respect to Sagittarius A* – the black hole our home galaxy hosts. The findings are published in Astrophysical Journal in 2018 August 2nd (2018, ApJ, 862, 150).

Color-composite images of the SMA map tracing the molecular gas of the CND (blue) and the Very Large Array (VLA) 6 cm map tracing the mini-spiral (red). The magnetic field of the JCMT-SCUPOL data and the model are overlaid with the white segments in the upper right and low left panel, respectively. The location of SgrA* is labeled with the black cross. The CND is a molecular torus (ring) rotating with respect to the supermassive black hole SgrA* in our Galaxy. The mini-spiral is hypothesized to be originated from the inner edge of the CND. The alignment of the magnetic field line along with the CND and the mini-spiral tells us that they are linked with a coherent magnetic field. The team found the magnetic field is able to guide the ionized particles from the CND to the mini-spiral, which suggests a picture the footprint of inflow near SgrA*. In the lower right panel, the latest dust polarization data taken in 2017 measured with the new instruments POL-2 installed in JCMT is shown. The magnetic field is shown with the white segments. An improved spatial coverage and sensitivity clearly reveal the connection between the CND and the mini-spiral at even higher spatial sampling than the JCMT-SCUPOL data, which confirm the picture the team proposed.


SgrA* – the best laboratory to study black hole feeding in the sky

Sagittarius A* (SgrA*),  being the closest SMBH in our home in the universe, the Milky Way Galaxy, has been targeted by many scientists to understand the nature of gas accretion in the past decades. Observing the gas accretion onto SMBH is critical to help us to understand how it releases tremendous energy.

The circumnuclear disk (CND) is a molecular torus rotating with respect to SgrA*, within which are the ionized gas streamers called mini-spiral (also called SgrA West) filling the molecular cavity. The mini-spiral is hypothesized to be originated from the inner edge of the CND. The CND, being the closest “food reservoir” of SgrA*, is therefore critical on the understanding of the feeding of SgrA*. However, looking for the physical evidences to connect the CND and the mini-spiral puzzles astronomers since they were discovered a few decades ago.

Intensive measurements of dynamical movements orbiting SgrA* have been done in the past decades, but another important force – the magnetic field – is rarely probed. This is solely because the weak polarized signal generated by the magnetic field from dust emission is difficult to measure. However, the magnetic field is expected to be important for material orbiting within and around the CND as the magnetic stress acting on the rotating disk can exert a torque to extract angular momentum from rotating gas, and thus drive gas inflows. Besides, The magnetic tension force is also possible to draw the gas back from the gravitational pull. Taking advantage of excellent atmospheric conditions of Mauna Kea summit at 4000 m, and large aperture size of the JCMT (15 m in diameter), the submillimeter polarization experiments were successfully obtained toward the Galactic Center to understand the role of magnetic field.

Tracing Magnetized Accreting Inflow

The team utilized the dust polarization data obtained by the JCMT-SCUPOL instrument to image the orientation of the magnetic field. A detailed comparison with higher-resolution interferometric maps from the Submillimeter Array (SMA) reveals that the magnetic field aligns with the CND.  Moreover, the innermost observed magnetic field lines also appear to trace and align with the mini-spiral coherently. This is the first attempt to reveal the footprint of inflow linking the CND and the mini-spiral since they were discovered a few decades ago. The comparison of the model and data reinforces the key idea that the CND and the mini-spiral can be treated as a coherent inflow-system.

The team found that the magnetic field is dynamically significant towards the CND and the mini-spiral. This finding tells us that the magnetic field is able to guide the motion of the ionized particles originated in the CND, and produce the observed spiral pattern of the mini-spiral. Dr. Hsieh said, “We found the magnetic field is critical to explain the inflow structure and will also help to understand the inflow picture in other galaxies hosting black hole similar to SgrA*. “

Paper and research team:

These observation results were published as Hsieh et al. “A Magnetic Field Connecting the Galactic Center Circumnuclear Disk with Streamers and Mini-spiral -Implications from 850 micron Polarization Data” in the Astrophysical Journal (published in the Astrophysical in August 2nd).

This research was conducted by:

Hsieh, Pei-Ying (ASIAA); Koch, Patrick M. (ASIAA); Kim, Woong-Tae (SNU); Ho, Paul T. P. (ASIAA; EAO); Tang, Ya-Wen (ASIAA); Wang, Hsiang-Hsu (CUHK)

This research is supported by the Ministry of Science and Technology (MoST) of Taiwan through the grants MoST 105-2811-M-001-141, MoST 106-2811-M-001-136, MoST 104-2119-M-001-019-MY3, MOST 105-2112-M-001-025-MY3, Academia Sinica Career Development Award, and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST; No. 3348-20160021).

Related Links:

https://sites.google.com/asiaa.sinica.edu.tw/newsite/ASIAA_TAIWAN_News/20180817

https://www.asiaa.sinica.edu.tw/news/shownews.php?i=0e2af7b8c43775f78802f11ca0063488

-20180816

RxA3m Retires

     We are only as good as the instruments we have. With this sentiment in mind, we make way for the next generation of instruments as we retire one of our long-serving heterodyne receivers, RxA3. 

RxA3m in the receiver cabin at JCMT

     RxA3 (http://www.eaobservatory.org/jcmt/instrumentation/heterodyne/rxa/) has been a stable source of great science for the JCMT since it was built by the Herzberg Institute of Astrophysics and delivered in 1998. It has served our JCMT user community well and the data collected from RxA3 will be utilized still for years to come. 

The GLT receiver installed at the JCMT when it was being tested in August 2017.

      With the retirement of RxA3, JCMT prepares for it’s replacement to arrive in January 2019 and hopes to be on sky by April 2019 in time for the next Event Horizon Telescope observing run. The replacement will be a three-receiver cryostat identical to that installed on the Greenland Telescope (GLT), and is estimated to be able to complete observations in approximately 1/4 of the time required by RxA3.
                      -2018/07/05

First observations of the magnetic field inside the Pillars of Creation: Results from the BISTRO survey

The BISTRO (B-Fields in Star-Forming Region Observations) Survey has for the first time mapped the magnetic field in the dense gas of the ‘Pillars of Creation’, using instruments on the James Clerk Maxwell Telescope (JCMT). The Pillars of Creation, in the Messier 16 star-forming region, which is also known as the Eagle Nebula, were the subject of one of the most iconic images taken by the Hubble Space Telescope (HST). The Pillars are a set of columns of cold, dense gas protruding into a region of hot, ionized plasma. The Pillars have nurseries of new stars forming at their tips, and are a particularly dramatic example of a feature found in many regions of interstellar space in which high-mass stars are forming.

We present the first high-resolution observations of the Pillars in polarized light at submillimeter wave- lengths – submillimeter light being on the cusp between infrared and radio waves, where the cold, dense dust and gas which will form the next generation of stars emits most of its light. Light emitted from these dusty regions is polarized perpendicular to the direction of its local magnetic field, and so we can use our observations to directly probe the magnetic field morphology within the dense gas of the Pillars of Creation. Our observations were taken at a wavelength of 0.85 mm as part of the BISTRO Survey, using the POL-2 polarimeter on the SCUBA-2 submillimeter camera at the JCMT. They show that the magnetic field runs along the length of the pillars, at a significantly different angle to the field in the surrounding ionized plasma, and has an estimated strength of approximately 170 − 320 microGauss (1.7 − 3.2 × 10−8 Tesla), an intermediate magnetic field strength for a region of space which is forming stars.

An illustrative figure of the BISTRO magnetic field vectors observed in the Pillars of Creation, overlaid on a HST 502 nm, 657 nm and 673 nm composite – HST imaging from Hester et al. (1996, AJ 111, 2349).

Young hot stars, with masses more than eight times that of the Sun, produce large numbers of high-energy photons. These high-energy photons ionize a volume of the region within which they form, splitting hydrogen atoms into pairs of protons and elections. As the shock front between the material ionized by the young stars and the untouched neutral material advances, complex structures form in the dense gas at the interface. Particularly, pillars of dense, neutral gas like those in M16 are found protruding into the ionized region, apparently left behind by the advancing shock front. The formation and evolution of these pillars is not well-understood – debate continues as to whether these pillars form behind obstructions to the shock front, or whether they can form from turbulent instabilities in the shock front itself. The role of the magnetic field in the formation of the Pillars is particularly uncertain, since the strength of the magnetic field in the dense parts of the Pillars has not been measured until now.

BISTRO magnetic field vectors overlaid on a HST 502 nm, 657 nm and 673 nm composite image of Pillar II. The magnetic field runs roughly parallel to the Pillar’s axis. No polarization is detected at the Pillar’s tip – this depolarization is consistent with a horseshoe-shaped magnetic field morphology on scales smaller than the beam.

Our observations of the magnetic field running along the length of the Pillars are consistent with the Pillars being formed by compression of gas with an initially weak magnetic field: the magnetic field has not had the strength to resist being dragged into its current configuration by the motions of the gas. However, the magnetic field strength appears to have been increased by being compressed in the forming pillars. The magnetic field strength that we estimate is large enough to magnetically support the sides of Pillars against collapsing radially under pressure from the surrounding hot plasma, and to prevent the Pillars collapsing under their own gravity. It is important to note though that the Pillars are still being destroyed by the same shock interaction that created them: the magnetic field that we measure is not strong enough to prevent the Pillars being gradually eroded from their tips by the effects of the young stars in the region. Our results suggest that the evolution and lifetime of the Pillars may thus be strongly influenced by the strength and orientation of their magnetic field: the Pillars’ longevity results from magnetic support.

Our proposed evolutionary scenario: (a) an ionization front moving perpendicular to the am- bient magnetic field approaches an existing over-density in the molecular gas. (b) The ionization front is slowed by the over-density. The flux-frozen magnetic field ‘bows’ into the forming pillar. (c) The com- pressed magnetic field supports the pillar against further gas-pressure- and gravity-driven radial collapse, but cannot support against longitudinal erosion of the over-density by ionizing photons. Throughout, dark blue shading represents molecular gas and light blue shading represents ionized material. The ionization front is shown as a black line. Grey dashed lines indicate the local magnetic field direction. Red arrows represent photon flux, black arrows represent magnetic pressure, and green arrows represent thermal gas pressure.

The James Clerk Maxwell Telescope, located on Mauna Kea in Hawaii, is operated by the East Asian Observatory. The BISTRO Survey is a large team of scientists working to understand the role of mag- netic fields in the formation of stars, with members from across the partner regions of the East Asian Observatory: China, Japan, South Korea, Taiwan and Vietnam, and from participating universities in the United Kingdom and Canada.

This research has been accepted for publication by The Astrophysical Journal Letters. A pre-print is available at http://arxiv.org/abs/1805.11554.

Kate Pattle, Derek Ward-Thompson, Tetsuo Hasegawa, Pierre Bastien, Woojin Kwon, Shih-Ping Lai, Keping Qiu, Ray Furuya, David Berry and the JCMT BISTRO Survey Team

Inquiries about this research: Email: kpattle@gapp.nthu.edu.tw

The “Pillars of Creation” is one of the most well-known images in astronomy, and it is very exciting to be able to add to what is known about this part of the sky.  The pillars are beautiful structures – remarkable for their highly coherent structure within the dynamic and highly energetic environment of a region forming high-mass stars.  We have found that the magnetic field within the Pillars is well-ordered, running along the length of the pillars, and is strong enough to influence the future evolution of the pillars, helping to support them against collapse.  This is an intriguing result because it shows us that the magnetic field is important to the region now, but also that it was likely not very important during the period when the pillars were forming.  The field appears to have changed significantly from its original direction to run along the pillars as they were formed by a shock interaction caused by nearby young stars.  This could not have happened if the magnetic field were strong enough to resist being moved.  Our results suggest that the importance of the magnetic field to the Pillars of Creation has evolved over time along with the Pillars themselves.

The JCMT is the only telescope in the world which could have made these observations – the JCMT’s POL-2 polarimeter and SCUBA-2 camera are a unique combination of instruments, observing at the wavelengths at which cold dust in star-forming regions emits most of its light.  POL-2 provides information on the magnetic field on the scale of objects such as the Pillars of Creation which is not available anywhere else.

We have already had a proposal accepted by the Submillimeter Array (SMA) on Mauna Kea to observe the magnetic field in the tips of the pillars in more detail.  In our JCMT observations we see the magnetic field disappear at the tips of the pillars.  This “depolarization” could be caused by tangled magnetic field lines or a complete reversal of magnetic field direction in the pillars’ tips causing the field to cancel out in our observations.  By observing at higher resolution with the SMA we will be able to see what the magnetic field looks like on these small scales, and to better understand what role the magnetic field is playing in the shock interaction which is driving the pillars’ evolution.  We could also potentially look in more detail still at the magnetic field in clumps in the pillars’ tips using the Atacama Millimeter/submillimeter Array (ALMA) in Chile, or observe the pillars in polarized near-infrared light using the airborne SOFIA observatory.

-2018/06/05

SMU Removal

Check out our hardworking staff carefully removing the Secondary Mirror Unit (SMU). JCMT is currently closed (2.5 weeks in May 2018) as the SMU undergoes some important maintenance. The basics of the work being done:
1. Chopper performance and XYZ tables measurements
2. Remove the chopper and service the SMU tables (strip down, clean, lubricate, change belts)
3. Reassemble SMU tables, reattach chopper and service (balance, vibrators, flex pivots, LVDTs, stingers)
4. Finalize and implement new zero points, rollover points, and limits
**Many thanks to our TSS Kevin Silva for putting together this awesome timelapse compilation.**

-20180514

International Women’s Day 2018


March 8th, 2018 was International Women’s Day. The EAO celebrated by hosting a special event at the ‘Imiloa Astronomy Center that gathered together all of the women who contribute to the Maunakea organizations. We strongly believe that the future of Maunakea lies in the hands of the young people of these islands. The bright and talented young women of our community are enabled and empowered by seeing women in successful roles at all levels of scientific, political and business enterprise. This event provided one more step, in what we hope will be many, towards gender equity in the Maunakea organizations and beyond. We are thrilled with the amount of support we received following the event. See below for links to articles and news features.

VIDEO: Maunakea Observatories Mark International Women’s Day

 

Hawaii News Now video: Maunakea Observatories honor International Women’s Day by Celebrating its Female Astronomers

Hawaii Tribune Herald article: Women Astronomers Hope to Inspire Girls to Take Up Science

Big Island Now article: Women of Hawai‘i Astronomy Community Gather to ‘Press for Progress’

– 20180315

Membrane back on!

January 10, 2018  The JCMT’s protective membrane is back in place after our month of commissioning without it. Now we can go back to observing in reasonable wind and during the daytime!

 

-20180111

18-month twinkle in a forming star suggests
 the existence of a very young planet

Discovery made possible by a leap in submillimetre radio astronomy technology,
 comparable to viewing videos instead of photos.

November 1, 2017 — An international team of researchers have found an infrequent variation in the brightness of a forming star. This 18-month recurring twinkle is not only an unexpected phenomenon for scientists, but its repeated behavior suggests the presence of a hidden planet.

This discovery is an early win for the James Clerk Maxwell Telescope (JCMT) Transient Survey, just one-and-a-half years into its three-year mandate to monitor eight galactic stellar nurseries for variations in the brightness of forming stars. This novel study is critical to understanding how stars and planets are assembled. The survey is led by Doug Johnstone, Research Officer at the National Research Council of Canada and Greg Herczeg, Professor at Peking University (China), and is supported by an international team of astronomers from Canada, China, Korea, Japan, Taiwan and the United Kingdom.

“This variation in the brightness or twinkle of the star EC53 suggests that something large is disrupting the gravitational pull of the forming star. The fact that it recurs every 18 months suggests that this influence is orbiting around the star – it’s quite likely a hidden, forming planet,” says Doug Johnstone. It is thought that a companion planet is orbiting the star, and its passing gravitational pull disrupts the rate of the gas falling onto the forming star, providing a variation in the observed brightness, or light curve, of the star.

 

Young stars are born in regions of the galaxy where molecular gas is abundant. When the star is young, gas and dust form a thick cloud that surrounds the star. Some of this material quickly flattens into a disk, in which planets will form. The cloud blocks the star itself from optical view, so astronomers study the star indirectly by using the cloud to learn details about the star growing inside. The star builds up its mass as gravity attracts gas to move from the disk onto the star, a process that also releases significant energy that heats up the surrounding gas cloud. Astronomers use telescopes sensitive to sub-millimetre wavelengths, like the JCMT, to measure the cloud brightness and reveal details about the growth of the star.

EC53’s light curve anomaly was discovered by Hyunju Yoo, graduate student at Chungnam National University and advisor Jeong-Eun Lee, Professor at Kyung Hee University (South Korea), through careful analysis of monthly observations of Serpens Main, a stellar nursery known to contain many forming stars. Although the brightness of EC53 has been observed to vary periodically at near-infrared wavelengths for some time, these sub-millimetre observations were essential in validating that the brightness variation was due to heating from gas accreting onto the forming star, rather than variations in the cloudiness of the environment.

“What caught my eye was a new round of data that showed a sudden brightness that hadn’t existed in previous observations,” says Lee. “I knew that something unique and interesting must be happening around this forming star. It turned out that it is indeed a very special object, providing a new window into how stars and planets form.”

A deeper understanding of the formation of stars and planets

For the remainder of the three-year sub-millimetre survey, the team will continue to monitor EC53 and will also be searching for additional young stars showing variations in growth to learn more about how stars and planets assemble. There are already a half-dozen additional candidate variables within the survey. By studying these stars, and using additional telescope facilities such as the powerful Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, the study will provide new and unique insight into the timescale for the formation of stars and planets, including whether planets form during or after the assembly of the star.

“This discovery marks a turning point; in a sense, it’s like sub-millimetre astronomy is moving from taking pictures of our galaxy to taking videos,” says Greg Herczeg. “The last 25 years have been devoted to perfecting observing techniques and instruments to allow us to see early star formation. But with recent advances in technology, we can now observe regions changing over time, for a deeper understanding of how stars form. This discovery is just one example of how much more we can now learn.”

Monitoring the brightness of forming stars over time using sub-millimetre wavelengths is an unconventional approach to observing that has been made possible by recent advances in imaging technology, like SCUBA-2, and data reduction processing which enables precise calibration and measurement.

The JCMT resides at the summit of Maunakea in Hawaii and is the largest single-dish sub- millimetre telescope in the world. The JCMT is operated by the East Asian Observatory, a partnership between China, Taiwan, South Korea and Japan, with support from the astronomy communities in Canada and the United Kingdom. The university-led contributions from Canada are supplemented by the NRC’s support for the JCMT archive at the Canadian Astronomy Data Centre.

This discovery has been accepted for publication in Astrophysical Journal and is available online.

This story is distributed on behalf of: The National Research Council of Canada, Peking University and Kyung Hee University.

Contacts

Media Relations Team
National Research Council of Canada
1-855-282-1637 (in Canada)
1-613-991-1431 (elsewhere in North America)
001-613-991-1431 (International)
media@nrc-cnrc.gc.ca
Twitter: @nrc_cnrc

The Kavli Institute for Astronomy and Astrophysics (KIAA)
Peking University
Shuyan Liu
+86-10-6275-6630
shuyan@pku.edu.cn

Kyung Hee University
Min-Jae Jung
Communications team
+82-10-6626-6694
ddubi17@khu.ac.kr

James Clerk Maxwell Telescope
Steve Mairs
1-808-969-6572
s.mairs@eaobservatory.org

– 20171101