September 14, 2015, just a few daysAfter the first LIGO switch on, a gravitational wave passed through the Earth. Like the billions of similar waves that have passed through the Earth throughout its history, this one was generated by the twisting, merging and collision of two massive ultra-distant objects far beyond our galaxy. From a distance of more than a billion light-years, we received a signal about the merger of two black holes. The signal, moving at the speed of light, finally reached the Earth.
And this time we were ready. Dual LIGO detectors saw how their arms expanded and contracted by a subatomic amount, but that was enough for the laser beam to move and produce an obvious change in the interference image. We first discovered a gravitational wave. Three years later, we already discovered eleven of these, ten of which came from black holes. Here is what we learned.
There were two “runs” of LIGO data: the first from September 12, 2015 to January 19, 2016 and the second, with improved sensitivity, from November 30, 2016 to August 25, 2017. The last launch, in particular, took place together with the VIRGO detector in Italy, which added not only a third detector, but also significantly improved our ability to mark the place of occurrence of these gravitational waves. LIGO is currently not working, closed for repairs with updates that will make it even more sensitive. A new data collection session should begin in the spring of 2019.
On November 30, the LIGO scientific collaboration announced the results of its improved analysis, which is sensitive to the last stages of the merger of objects with masses from 1 to 100 solar.
Of the 11 discoveries that were made toAt present, 10 represent the fusion of black holes, and only GW170817 represents the fusion of neutron stars. The fusion of neutron stars occurred closest to us - only 130-140 million light years. The most massive merger - GW170729 - we heard from a distance of 9 billion years.
These two findings also represent the mostthe lightest and heaviest fusion with the formation of gravitational waves: neutron stars with a mass of 1.46 and 1.27 solar masses collided in GW170817, and black holes with a mass of 50.6 and 34.3 solar masses collided in GW170729.
Here are five amazing facts that we learned through all these discoveries.
- eleven. Big is not always visible better
- 2 # 2. More detectors are better.
- 3 # 3. Black Hole Merging Illuminates the Universe
- 4 # 4. Power generators
- 5 # 5. More smaller - coming soon
#one. Big is not always visible better
The largest black hole merger is the easiestto see - and they are not more than 50 solar masses. Gravitational waves are good in that they are easier to see from afar than a light source. Light loses brightness in proportion to the square of the distance: a star that is ten times farther away will be a hundred times dimmer. But gravitational waves decay in direct proportion to the distance: black holes that are at such a distance will produce 1/10, and not 1/100, of the signal strength.
As a result of this, we can see verymassive objects at very large distances, but we don’t see black holes merging at 75, 100, 150 or 200+ solar masses. From 20 to 50 solar masses are quite common, but so far we have not seen anything above it. Perhaps black holes arising from supermassive stars are indeed rare.
# 2 More detectors are better.
Adding a third detector at the same timeimproves the ability to determine the position of objects and increases the detection frequency. LIGO worked for about 4 months during the first launch and 9 months during the second. Nevertheless, half of their discoveries occurred in the last month: VIRGO worked with it. In 2017, gravitational wave events were detected these days:
- July 29 (black holes of solar masses 50.6 and 34.3),
- August 9 (black holes of solar masses 35.2 and 23.8),
- August 14 (black holes of solar masses 30.7 and 25.3),
- August 17 (neutron stars of solar masses 1.46 and 1.27),
- August 18 (black holes of solar masses 35.5 and 26.8),
- August 23 (black holes of solar masses 39.6 and 29.4).
During this last month of observation, wefound mergers more than once a week. Maybe when we become sensitive to large distances and signals of smaller amplitudes and masses, we will begin to see one event a day in 2019.
# 3 Black Hole Merging Illuminates the Universe
When the black holes we foundcollided, they released more energy at its peak than all the stars in the universe combined. Our Sun is the standard that shapes our view of the rest of the stars. It shines so brightly that its total energy production - 4 x 1026 W - is equivalent to turning four million tons of matter into clean energy every second.
With an estimate of ~ 1023 stars in the observable Universe,the total output power of all stars shining in the sky exceeds 1049 watts at any given time: a huge amount of energy is distributed throughout the cosmos. But within a few milliseconds during the peak of the merger of double black holes, each of the 10 observed events, in terms of energy, overshadowed all the stars in the Universe combined. (Although this amount is relatively small). Not surprisingly, the most massive mergers topped this list.
#four. Power generators
About 5% of the total mass of both black holesconverted into clean energy according to Einstein’s formula E = mc2 during these mergers. The ripples in space that these black hole mergers produce must come from somewhere and must somehow come from the mass of the black holes merging themselves. On average, based on the magnitude of the signals of gravitational waves that we saw and the restored distances to them, black holes lose about 5% of their total mass, which turns into gravitational-wave energy, when merged.
- GW170608, the fusion of black holes with the lowest mass, converted 0.9 solar masses into energy.
- GW150914, the first radiance of black holes, converted 3.1 solar masses into energy.
- GW170729, the most massive black hole fusion, has converted 4.8 solar masses into energy.
These ripple events inspace-time are the most energetic events known since the Big Bang. They produce more energy than any fusion of neutron stars, gamma-ray bursts or supernovae.
#5. More smaller - coming soon
With all that we have seen so farwe can expect that we will see the merging of black holes with a lower mass and a higher frequency. The most massive black hole fusions produce signals with the largest amplitude, so they are easiest to detect. But given how volume and distance are related, a twice as large distance means eight times as much volume. The more sensitive LIGO becomes, the easier it is to detect massive objects at large distances than low-mass objects nearby.
We know that there are black holes in 7, 10, 15or 20 solar masses, but LIGO is easier to spot a more massive black hole away. We expect that there are double black holes with diverging masses: one of them will be much more massive than the other. As our sensitivity improves, we expect that there will be more, but it will be easiest to find the most massive ones. We expect that the most massive of them will dominate the first discoveries, just as the “hot Jupiters” dominated the first searches for exoplanets. As we improve the search process, we will find more black holes with less mass.
When the discovery was announced firstgravitational wave, along with this, gravitational wave astronomy was born. People compared this event to when Galileo first sent his telescope to heaven, but in reality it is much more. It was as if our skies were covered with clouds, and we first developed a device that allows us to see through them a sufficiently bright source of gravity: the fusion of black holes or neutron stars. The future of gravitational wave astronomy promises to revolutionize our understanding of the universe, to show it in a new light. And this future has already arrived.
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