JAXA Spacecraft Hitomi Gives Revolutionary View of Galaxy Cluster

by Sankalan Baidya
JAXA Spacecraft Hitomi

JAXA Spacecraft Hitomi that met its unfortunate doom in April this year has given some extraordinary information on Galaxy Group. For long, scientists have wondered why unexpectedly fewer numbers of stars are formed in galaxy groups. Galaxy groups are huge. They contain hundreds and thousands of galaxies. Logically, they should give birth to huge numbers of stars. Unfortunately, that’s not the case. But why?

What Did JAXA Spacecraft Hitomi Study in Galaxy Cluster?

It seems that the doomed JAXA Spacecraft Hitomi gave an answer to this question before it disintegrated. According to Andrew Fabian, astronomy professor in University of Cambridge, the measurements made by Hitomi while looking at Perseus Galaxy Cluster were of unprecedented precision. According to Fabian, the measurements were 50x more accurate compared to measurements given by any previous instrument.

What Hitomi did was to measure the gas motion in the Perseus Cluster. The supermassive black hole that sits at the center of the Perseus Cluster is stirring the gas in the cluster and is preventing it from cooling down. Since the gas cannot cool down, it cannot give birth to stars. Fabian says that if the black hole didn’t mix up the gas as it is doing, the central galaxy of the cluster would have had much higher stellar mass. It would also have been much brighter!

Professor Andrew Fabian is the chairperson of a part of Science Working Group of Hitomi. The group consists of international members and the whole group is headed by JAXA. This group published the findings of Hitomi. Interestingly that’s the only science Hitomi managed to complete before its destruction.

According to Norbert Werner, research associate in California’s Stanford University, it was already known that supermassive black holes sit at the center of every single galaxy cluster. These black holes have a mass of tens of billions of our Sun. Werner says that it was known to us that these black holes injected energy into the gas and prevented star formation by cooling down of the gas. Hitomi’s observations, according to Werner, now gives us a better understanding of the whole mechanism. The black hole stirs the gas just to the right amount so that star formation is prevented.

What Precisely JAXA Spacecraft Hitomi Observed?

Galaxy clusters are really big. They can contain anywhere between 50 galaxies to thousands of galaxies. Nearly 15% of each such cluster is made of hot gas. The gas can reach millions of degrees Fahrenheit in temperature. When viewed in X-Ray spectrum, this gas shines brightly. Making an estimate of the amount of gas can give an estimate of how big a galaxy cluster is. However, getting an accurate estimate of gas content is not possible because gas in these clusters is constantly stirred up. Not only that, stars are also born out the gas, thereby quickly changing gas volume.

JAXA Spacecraft Hitomi

Image showing supermassive black hole heating up intergalactic gas and thereby preventing formation of stars. Credit: SLAC National Accelerator Laboratory

Perseus cluster is the brightest cluster in sky when viewed in X-Ray spectrum. It is also one of the biggest clusters out there. Several instruments were previously used to study the Perseus cluster. They all revealed gigantic gas bubbles. These bubbles were spat out by the cluster’s central supermassive black hole. How big are these gas bubbles? They are thousands of light years wide.

JAXA spacecraft Hitomi also observed the same. However, it did something extra. It linked the gas movement to these bubbles. The bubbles rise out from the black hole and they suck up gas from the cluster’s center. This action stirs the gas and in the process, heats it up. As a result of this action, gas cannot cool down. Images in visible light spectrum show that cold gas form cluster center is pulled up by the bubbles.

Comments by Roger Blandford on Observations of JAXA Spacecraft Hitomi

Roger Blandford is professor of physics as Stanford University. He is also a particle physics and astrophysics professor of SLAC National Accelerator Laboratory of Department of Energy. Blandford has been assigned as co-principal investigator of Hitomi.

According to Blandford, the gas is heated up by the motion of the gas but the gas travels at a speed of just 100 miles a second. This is way too slow compared to the disturbance (when looked at X-Ray imaged) that are found in the region. According to him, understanding the movements of the gas will definitely impact the estimates made about the mass of the gas. However, the calculations based on Hitomi’s observations didn’t lead to any major changes the mass calculations made earlier.

Andrew Fabian said that since Hitomi did not survive, scientists are currently unable to make same calculations for other galaxy clusters. This means that operation of the feedback process cannot be properly understood.

The whole research was published in the journal Nature on July 6, 2016.

A Bit About JAXA Spacecraft Hitomi

JAXA spacecraft Hitomi was launched back in February 2016. Onboard was an X-Ray detector. The detector was extremely powerful. Way more powerful than any launched in outer space earlier. It was capable of detecting object that were 10 times to 100 times fainter compared to objects detected earlier.

Hitomi was designed for probing supernova remnants, galaxy clusters, black holes and other high energy object in the gamma ray and X-ray wavelengths. In just over a month in the deep void, Hitomi was lost – thanks to software programming flaw. As a result of the flaw, the satellite went into a state of uncontrollable spin. The spin caused many of its parts to snap off. JAXA stopped all attempts to establish contacts with Hitomi by end of April and thereby ending the supposed 3-year mission.

However, Hitomi did some science stuff. 3 days of its first week in void, Hitomi was busy observing the Perseus cluster. A total of 4 observations were made. According to Andrew Fabian, if Hitomi didn’t meet its tragic end, it would have successfully mapped majority of the Perseus cluster in a month’s time or a little more than that.

According to Irina Zhuravleva, co-author of the study published on Hitomi’s finding, Hitomi started a whole new chapter in world of X-ray astronomy. Irina, who is from Kavli Institute for Particle Astrophysics and Cosmology, said: “Being able to measure gas motions is a major advance in understanding the dynamic behavior of galaxy clusters and its ties to cosmic evolution.”

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