ALMA observes a giant sunspot (1.25 millimetres)
ALMA observes a giant sunspot (3 millimetres)
ALMA observes the full solar disc
Image of the solar surface alongside a close-up view of a sunspot from ALMA
Videos
ESOcast 92 Light: ALMA Starts Observing the Sun
Comparison of the solar disc in ultraviolet and millimetre wavelength light
New images taken with the Atacama Large
Millimeter/submillimeter Array (ALMA) in Chile have revealed otherwise
invisible details of our Sun, including a new view of the dark,
contorted centre of a sunspot that is nearly twice the diameter of the
Earth. The images are the first ever made of the Sun with a facility
where ESO is a partner. The results are an important expansion of the
range of observations that can be used to probe the physics of our
nearest star. The ALMA antennas had been carefully designed so they
could image the Sun without being damaged by the intense heat of the
focussed light.
Astronomers have harnessed ALMA's capabilities to image the millimetre-wavelength light emitted by the Sun’s chromosphere — the region that lies just above the photosphere,
which forms the visible surface of the Sun. The solar campaign team, an
international group of astronomers with members from Europe, North
America and East Asia [1],
produced the images as a demonstration of ALMA’s ability to study solar
activity at longer wavelengths of light than are typically available to
solar observatories on Earth.
Astronomers have studied the Sun and probed its dynamic surface and
energetic atmosphere in many ways through the centuries. But, to achieve
a fuller understanding, astronomers need to study it across the entire
electromagnetic spectrum, including the millimetre and submillimetre
portion that ALMA can observe.
Since the Sun is many billions of times brighter than the faint
objects ALMA typically observes, the ALMA antennas were specially
designed to allow them to image the Sun in exquisite detail using the
technique of radio interferometry — and avoid damage from the intense
heat of the focussed sunlight [2].
The result of this work is a series of images that demonstrate ALMA’s
unique vision and ability to study our Sun.The data from the solar
observing campaign are being released this week to the worldwide
astronomical community for further study and analysis.
The team observed an enormous sunspot
at wavelengths of 1.25 millimetres and 3 millimetres using two of
ALMA's receiver bands. The images reveal differences in temperature
between parts of the Sun's chromosphere [3].
Understanding the heating and dynamics of the chromosphere are key
areas of research that will be addressed in the future using ALMA.
Sunspots are transient features that occur in regions where the Sun's
magnetic field is extremely concentrated and powerful. They are lower
in temperature than the surrounding regions, which is why they appear
relatively dark.
The difference in appearance between the two images is due to the
different wavelengths of emitted light being observed. Observations at
shorter wavelengths are able to probe deeper into the Sun, meaning the
1.25 millimetre images show a layer of the chromosphere that is deeper,
and therefore closer to the photosphere, than those made at a wavelength
of 3 millimetres.
ALMA is the first facility where ESO is a partner that allows
astronomers to study the nearest star, our own Sun. All other existing
and past ESO facilities need to be protected from the intense solar
radiation to avoid damage. The new ALMA capabilities will expand the ESO
community to include solar astronomers.
Notes
[1] The ALMA Solar Campaign team includes: Shin'ichiro Asayama, East
Asia ALMA Support Center, Tokyo, Japan; Miroslav Barta, Astronomical
Institute of the Czech Academy of Sciences, Ondrejov, Czech
Republic; Tim Bastian, National Radio Astronomy Observatory, USA; Roman
Brajsa, Hvar Observatory, Faculty of Geodesy, University of Zagreb,
Croatia; Bin Chen, New Jersey Institute of Technology, USA; Bart De
Pontieu, LMSAL, USA; Gregory Fleishman, New Jersey Institute of
Technology, USA; Dale Gary, New Jersey Institute of Technology,
USA; Antonio Hales, Joint ALMA Observatory, Chile; Akihiko Hirota, Joint
ALMA Observatory, Chile; Hugh Hudson, School of Physics and Astronomy,
University of Glasgow, UK; Richard Hills, Cavendish Laboratory,
Cambridge, UK; Kazumasa Iwai, National Institute of Information and
Communications Technology, Japan; Sujin Kim, Korea Astronomy and Space
Science Institute, Daejeon, Republic of Korea; Neil Philips, Joint ALMA
Observatory, Chile; Tsuyoshi Sawada, Joint ALMA Observatory,
Chile; Masumi Shimojo (interferometry lead), NAOJ, Tokyo, Japan; Giorgio
Siringo, Joint ALMA Observatory, Chile; Ivica Skokic, Astronomical
Institute of the Czech Academy of Sciences, Ondrejov, Czech
Republic; Sven Wedemeyer, Institute of Theoretical Astrophysics,
University of Oslo, Norway; Stephen White (single dish lead), AFRL,
USA; Pavel Yagoubov, ESO, Garching, Germany and Yihua Yan, NAO, Chinese
Academy of Sciences, Beijing, China.
[2] Indeed, this lesson has been learned the hard way: the Swedish–ESO Submillimetre Telescope (SEST) had a fire in its secondary mirror assembly after the telescope was accidentally pointed at the Sun.
[3] A map of the whole disc of the Sun
was also made with a single ALMA antenna, using a technique called
fast-scanning, at a wavelength of 1.25 millimetres. The accuracy and
speed of observing with a single ALMA antenna makes it possible to
produce a map of the entire solar disc in just a few minutes. These maps
show the distribution of temperatures in the chromosphere over the
whole disc at low spatial resolution and therefore complement the
detailed interferometric images of individual regions of interest.
More Information
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.
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. 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, the world’s most advanced visible-light astronomical
observatory and two survey telescopes. VISTA works in the infrared and
is the world’s largest survey telescope and the VLT Survey Telescope is
the largest telescope designed to exclusively survey the skies in
visible light. ESO is a major partner in ALMA, the largest astronomical
project in existence. And on Cerro Armazones, close to Paranal, ESO is
building the 39-metre European Extremely Large Telescope, the E-ELT,
which will become “the world’s biggest eye on the sky”.
Links
Contacts
Roman Brajsa
Hvar Observatory
University of Zagreb, Croatia
Tel: + 385 1 4639 318
Cell: + 385 99 2619 825
Email: romanb@geof.hr
Ivica Skokic
Astronomical Institute of the Czech Academy of Sciences
Ondrejov, Czech Republic
Tel: + 420 323 620 133
Cell: + 385 91 890 5815
Email: ivica.skokic@asu.cas.cz
Richard Hook
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591
Email: rhook@eso.org
Source: ESO
