What aspect of Powehi appeals to you the most? Are you interested in the Kumulipo – the Hawaiian creation chant that is the origin of the name which translates to English as "the adorned fathomless dark creation".

Are you impressed by the progress of women in science exemplified by the image maker? Are you someone who looks into the night sky wondering what is going on out there? Are you a techno addict who wants to be amazed by how the image was made? Do you want to know what that image really shows?

I am a knowledge junkie and, with all of these questions being woven through the image of a black hole that we have seen recently, I am on a high.

In 2015, the Hawaiian Supreme Court invalidated a permit to build a huge telescope costing about $1.5 billion on the top of Mauna Kea. The court decided that native Hawaiians who regard the peak as sacred had not been given the opportunity to make their feelings known during the permit procedure.


In October 2018, after much discussion between the various parties, the Hawaiian Supreme Court granted building consent. This telescope will be totally different to those that imaged Powehi but the fact that Hawaiian language Professor Larry Kimura give this name is hopeful for the coming together of cultures.

Katie Bouman is the young woman who led the team that created the computer algorithm used to bring together the 5 petabytes of data (equivalent to about 10,000 500Gb hard drives) into a meaningful picture.

You may have heard the comments about how women are now taking a full part in astronomy. The true story is much worse. Women have been involved in astronomy for a long time. They have simply not been visible.

Henrietta Swan Leavitt examined thousands of astronomical photographs in order to discover the luminosity-period relationship for Cepheid variable stars (if you are interested you can Google what this is all about).

This formed the base line for the work of Edwin Hubble and his idea of the expanding universe (the Big Bang as Fred Hoyle called it). Ms Swan Leavitt and other women who did the donkey work of the calculations were referred to as "computers" in the accounts of Hubble's work.

When William Herschel discovered the planet Uranus in March 1781, it was his sister Caroline who recorded the observations he dictated from the telescope and it was she who did much of the construction of the telescope. Her later work resulted in a more mathematical approach to astronomy. She is rarely mentioned in accounts of the work.

Vera Rubin graduated at the highest possible level in her astronomy degree in 1948 but was not accepted into Princeton because she was female. Instead she entered Cornell, where she researched the motion of spiral galaxies.

Her research showed that the strength of the gravity in these galaxies was much greater than could be explained by the visible matter. In the 1960s she suggested the presence of matter in a form that could not be detected by telescopes. She was largely ignored. Research in the past 20 years has shown her findings to be correct, with the coining of the term "dark matter", but she was not given any credit for almost 30 years after her original work.


We can only hope that the recognition of Katie Bouman as the maker of the image is not eclipsed because of her gender.

It is the middle of April. If you find a place where you can get a clear view of the northern sky and the moon has set, you will see a bright red star fairly low down and a bit to the east of north.

This is Arcturus. The light entering your eyes set off in 1982. Higher up and a bit to the left (west) is a bright white star. This is Spica. The light you see left Spica in 1756, 13 years before Cook first visited Aotearoa. Using these two stars imagine an equilateral triangle pointing west and down a bit. The third corner of the triangle falls in a blank piece of sky.

With a good pair of binoculars, you may see several small dim fuzzy patches in this area. These are galaxies outside our Milky Way galaxy. The light you see set off about the time the dinosaurs were going extinct 60–65 million years ago.

Charles Messier made a catalogue of these objects, giving each one a number. The galaxy which interests us here is M87. Circumstantial evidence suggests that most galaxies have a black hole at their centre and the one in M87 is big, with a mass between 2000 billion and 3000 billion times the mass of the Sun.

Until recently it had not been seen directly. The reason is the distance. Although it is big enough to hold the entire solar system, trying to see what it looks like is equivalent to trying to count the dimples on a golf ball on the surface of the moon. So here comes the bit for the techy freaks.

Our own town telescope has an object glass 24 cm in diameter. It is great for looking at the craters on the Moon and the rings of Saturn. So why can we not simply put a more powerful eyepiece on it and see the black hole in M87?

The problem is the nature of light. Light is a wave and this puts physical limits on the detail that can be seen using a telescope. The longer the wavelength of the light the less the detail, and the greater the diameter of the telescope the greater the detail.

The telescope to be built on Mona Kea will have a diameter of 30 metres which is 125 times the diameter of the Whanganui telescope, so detail 125 times smaller will be visible.

In fact, because of the relative quality of the optics, local atmospheric conditions and the use of adaptive optics on the large telescope the effective difference will be closer to a factor of 1000 or more.

M87 the galaxy that contains the black hole. Photo / Supplied
M87 the galaxy that contains the black hole. Photo / Supplied

But this is not big enough to image the black hole. To get any definition at all will require a telescope of several thousand kilometres in diameter. Obviously we cannot build such a device. We can however, use a trick called long-baseline interferometry.

Put simply, data from many radio telescopes pointed at the black hole but separated by the diameter of the earth is combined to effectively give a virtual telescope with a diameter equal to the diameter of the earth. It has taken 10 years to get this to work and the computer skills of Katie Bouman and her colleagues to bring the huge amount of data together in a meaningful form.

So, what are we actually seeing in the picture? We are not seeing a black hole. A black hole is an area in space where mass has become so concentrated that the gravitational field stops even light getting out – hence black hole.

With the strong gravitational field, matter is pulled into an orbiting accretion disc around the black hole. The matter in the accretion disc is moving at speeds close to the speed of light and is incredibly hot with temperatures in the millions of degrees Centigrade. What we are seeing in the image is electromagnetic radiation from the accretion disc.

Matter in the accretion disc gradually falls towards the black hole and eventually passes the event horizon. The event horizon is the point where the gravity becomes so strong that even light cannot escape.

The dark area in the centre of the image is where the matter vanishes beyond the event horizon. Within the event horizon we are unlikely ever to know exactly what happens. Theory suggests that time gradually slows to a halt, but mathematics has trouble dealing with this area.

But there is more fun. Space and time just outside the event horizon are so distorted by the gravitational effects that light, following what would look like a straight line if you could get close enough to see (do not try this at home) can bend around and leave in the opposite direction.

This means that from whatever direction you are looking at the object, you are seeing light from the opposite side as well as the near side.

In the image one side (bottom) looks brighter than the other. This is an effect called relativistic beaming. The matter in the accretion disc is moving away at the top and towards us at the bottom. Because the speeds are so huge (perhaps 500,000,000 kilometres per hour) the matter moving towards us appears brighter.

In January you may have read my article about gravity waves. Although we take gravity for granted as a part of everyday life that keeps us on the ground it is much less well understood than the other fundamental forces of physics.

With the technology to begin to image the effects of extreme gravity around black holes and detect gravity waves we are on the edge of a whole new adventure in scientific discovery.