Michitoshi Yoshida, astronomy

“People might think the sky is constant and astronomers are always looking at the same things, but the universe is active and so dynamic.  All the time there is some explosion happening somewhere.  Every time we look at the sky there is something new to see.”

The First Telescope

“We were up on the roof for class experiments during my third year of university and we needed to observe the stars through tiny telescopes.  That’s what lit the fire in my heart.”


Professor Michitoshi Yoshida remembers his first introduction to astronomy with a genuine fondness.  That evening on the university roof has led to his current position at the Hiroshima Astrophysical Science Center, searching galaxies several hundred million light years away from the Milky Way for a variety of astronomical phenomena, including potential sources of gravitational waves.  However tiny the first telescope was, his first scientific interests as a student started on a significantly smaller scale.


“In high school, I was very interested in particle physics.  But when I went to university it was so difficult.  The star observation experiment was the trigger for me to decide that I would be an astronomer.  My study of particle physics was very useful, because nuclear fission reactions between small particles power the sun and most other stars.”


The complications of observing the reactions responsible for the formation of stars in other galaxies require modern astronomers to constantly create new tools.  Creating and maintaining equipment has been a constant through Yoshida’s multiple career re-focuses onto different areas of astronomy.


Building New Instruments

He began his research career in the 1990s at the Okayama Astrophysical Observatory, a branch of The National Astronomical Observatory of Japan, searching the universe for highly active galaxies.  Studies of active galaxies, ones that either produce many new stars or send high-energy emissions out into space, can reveal how stars form and how galaxies evolve.  Another aspect of Yoshida’s work was to build equipment for the Subaru Telescope.


“I think observational astronomy is a part of experimental physics.  We want to know some specific characteristics or properties of particular astronomical objects, so we need very specialized and dedicated instruments to get the best information from the object.  We must customize the instruments or develop some new kind of instrument from scratch.”


Technological improvements mean that astronomers like Distinguished Professor Michitoshi Yoshida can specialize in both optical and near infrared studies. Previous generations of astronomers were divided based on what wavelengths of light their experiments used to examine the university.

Yoshida refers to himself as an optical and near-infrared astronomer, meaning his work involves wavelengths of light that can be seen by the human eye as well as wavelengths that are too long to be seen.  These types of astronomy used to be separate fields requiring separate telescopes, but technological advances are reducing the divide.


“Optical and infrared astronomy are becoming more and more similar in what we can detect.  Infrared detectors are becoming as advanced as the visual sensors in optical telescopes, which are like very big, very sensitive digital cameras,” Yoshida says, referencing the CCD or Charge Capital Device visual chips in most modern cameras.


“Developing the instrument – that by itself is my pleasure.  If we get some information from the astronomical object with my own instrument, that is also very much my pleasure.”



“But recently, I am interested in gravitational waves,” Yoshida says, switching the topic to Einstein and the theory of general relativity.


The theory is that when massive objects orbit each other, their interaction violently distorts space-time and creates ripples that permeate throughout the universe.  Certain transient objects are massive enough that their interactions could produce such ripples, or gravitational waves.


Einstein described general relativity nearly 100 years ago, but only in 2015 did researchers detect gravitational waves using the Advanced-LIGO, Laser Interferometer Gravitational-Wave Observatory, telescope in America.  In late 2015, the telescope made two separate observations of what scientists suspected were gravitational waves and astronomers around the world were notified.

Distinguished Professor Michitoshi Yoshida telling the story of how he and his Hiroshima University colleagues received the first gravitational wave detection alert from the Advanced-LIGO telescope.

“The first alert came at maybe four or five in the morning, so I woke up about two hours later and I saw the e-mail.  The message says maybe there is a gravitational wave event. ‘Maybe?’ If the experts at LIGO are not certain, what should I do with ‘Maybe?’  My colleagues and I conferred here at Hiroshima University, and we decided we should try with our telescope to see if there is anything that could be making gravitational waves,” recalls Yoshida.


The Advanced-LIGO telescope can only detect gravitational waves, not observe their source.  The alert system mobilizes astronomers around the world to point their telescopes in the direction of where the waves have been detected and scan the sky to try to identify what is responsible for the waves.


The current technology of Advanced-LIGO can only locate a suspected gravitational wave event to an area of 100 to 500 square degrees of the sky.  For comparison, the entire Orion constellation covers approximately 595 square degrees.  Yoshida says of this lack of specification, “Oh. So, where should I look?”


This broad area of sky is too large for researchers to meticulously scan with any reasonable chance of finding the source of the waves, particularly given the short time span when the objects might remain visible.  Supernovae, gamma ray bursts, or two neutron stars merging can all create gravitational waves, but the light coming from those events is detectable for only about five days after it occurs, an incredibly short time span in astronomical terms.


“These events are so short, so it is very exciting.  We must be fast!  Quick observation is most important,” says Yoshida.


Knowing what is responsible for the waves is essential if researchers are to develop a better understanding of the universe after detecting the waves.


“The location of the first event was not in a good part of the sky to see from Japan, but we tried anyway and we also asked the telescope in New Zealand to look.  Later, other researchers determined the waves were from a merger of two black holes, which we would not see with our telescopes anyway,” says Yoshida.


The telescope in New Zealand Yoshida refers to, the Mount John University Observatory, is part of a network of telescopes wholly or partially managed by Japanese universities as part of international collaborations.  The network also includes five telescopes in Japan, the Subaru telescope in Hawaii, the Infrared Survey Facility in South Africa, and the Atacama Large Millimeter Array in Chile.


“The second LIGO alert came at about two in the afternoon on December 27, 2015.  My colleagues and I were at work, and at first we wondered, maybe this is part of a joke for Christmas.  But the area of the sky was a good location to scan from Japan, so all five telescopes in Japan looked.  We even were granted some time to use Subaru ten days later, but that would probably be too late and anyway, the source turned out to be more black holes.  Now LIGO is shut down for improvements, so we know there will be no alerts.  But maybe later this year when LIGO is turned on again we can try.”



The search for sources of gravitational waves is a recent addition to Yoshida’s career developing tools to study the evolution of galaxies and the unpredictable or short-lived events that shape them.  After the Subaru Telescope was installed in Hawaii in 1999, Yoshida was assigned as Director of the Okayama Astrophysical Observatory, working there from 2000 to 2009.  During that time, while managing and maintaining the observatory, Yoshida refocused his own research specialty to the search for extra solar planets and understanding transient astronomical objects.


“Every day we needed to do maintenance work to keep the telescope in the best possible working condition.  Plus, I had two research projects, so every day was very busy.”


Transient phenomena include any object that becomes intensely bright in any wavelength of light suddenly and unexpectedly.  Gamma ray bursts, cataclysmic variable stars, and supernovae are all transient phenomena that can reveal information about how stars and galaxies evolve, as well as the physics governing the universe.  The energy within these reactions is so extreme that they cannot be reproduced by ground-based experiments.


Kantana Telescope

The 1.5 meter Kantana Telescope is used by Hiroshima University astronomers.

The Hiroshima Astrophysical Science Center focuses on the search for transient objects, making it a natural location for Yoshida to continue his research using the 1.5-meter Kanata Telescope at Hiroshima University.  Additionally, when he arrived at Hiroshima in 2010 he returned to his first interest in extra galactic astronomy.



Professor Michitoshi Yoshida explaining the fast collisions between galaxies and the intra-cluster medium that strip gas from the galaxies. This research can reveal the physical processes of how environmental conditions affect galaxy evolution.

Pointing to an image of a black sky filled with different sized bright spots, Yoshida explains that all the bright, white points are individual galaxies and the red or orange streak darting out of one galaxy is gas that has been removed from the galaxies.  These active galaxies that Yoshida studies frequently form new stars and can be 300 million light years away.  Stars are formed from interstellar gas.  If a galaxy were to lose all of its gas, star formation inside that galaxy would stop.



Every white or yellow spot is a unique galaxy. The red haze coming from the galaxy at the top of the image is gas being stripped out of the galaxy and entering the intergalactic space, an action caused by gravitational interactions with other galaxies. This image is a research photo including the galaxy IC4040 in the Coma Galaxy Cluster. The original research article where this photo was published can be found using the following citation information: Yoshida M., Yagi M., Komiyama Y., et al. “Kinematics and excitation of the ram pressure stripped ionized gas filaments in the Coma cluster of galaxies.” 2012, The Astrophysical Journal, 749, 43. http://dx.doi.org/10.1088/0004-637X/749/1/43


It is uncommon for galaxies to expel their gas, but if many galaxies are clustered together, some may interact as they continuously move towards the center of the cluster, attracted by the gravity of other galaxies.  The tidal force between the galaxies and the pressure of high-speed collisions between galaxies and free-floating gas can strip gas out of the galaxies.  This type of collision likely created the red and orange streaks in the telescope image.


The so-called “rich clusters” of galaxies that Yoshida studies include at least 1,000 individual galaxies of varying activity levels.  The conditions that cause the gas removal phenomenon exist in every cluster, meaning that understanding the causes and effects could shed light on how the environments surrounding galaxies affect their evolution.


New Things to See

More tools to understand and identify astronomical events are always in the process of becoming available.  By the time the Advanced-LIGO telescope is active again, Yoshida hopes that Hiroshima University will have a new telescope located in Tibet to search for the cause of gravitational waves.  Astronomers compete for time to use many of the world’s telescopes, meaning observations can be scheduled sometimes years in advance.  The unpredictable and poorly understood nature of gravitational waves means it is essential to have telescopes that are usually available for regular experiments, but can prioritize the search for gravitational wave sources whenever an alert arrives.


“When I visit Tibet to prepare the telescope, the altitude and the paperwork is a problem.  But the telescope’s instruments will be very good,” Yoshida says with smile.


Throughout his career, Distinguished Professor Michitoshi Yoshida has built instruments for telescopes now located in Hawaii, Japan, and soon in Tibet.

New telescopes provide improved tools for looking at well-known astronomical phenomena that remain poorly understood and give astronomers the potential to identify current events throughout the universe.


“People might think the sky is constant and astronomers are always looking at the same things, but the universe is active and so dynamic.  All the time there is some explosion happening somewhere.  Every time we look at the sky there is something new to see.”



This interview and article was originally written in July 2016 by Caitlin E. Devor, of the Hiroshima University Research Planning Office.  Photos by Hiroshima University Public Relations Group.  Please provide attribution to Hiroshima University if reusing any of this content.



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