Modifications of supernova type 1a

Star explosions known as type 1a supernovae have long been used as a 'standard candle', their constant brightness is a way for astronomers to measure the distance of the universe and the expansion of the universe. However, a new study published this week in Nature shows that the sources of variation of type 1 supernovae will need to be taken into account if astronomers want to use them for more accurate measurements. Future.

The discovery of dark energy, a mysterious force that accelerates the expansion of the universe, is based on Type 1a supernova observations. But to explore the nature of dark energy and determine if it changes or does not change over time, scientists will need to measure the cosmic distance with much higher accuracy than before.

The lead author Daniel Kasen, a postdoctoral researcher at the University of California, Santa Cruz, said: 'When we begin the next generation of cosmological experiments, we will need to use the Type 1a crystals as a very sensitive distance measuring tool. We know that their brightness is not exactly the same, but there are several ways to adjust this. But we need to know if there are systematic differences that can distort the distance measurement. This research has figured out what makes such a difference in brightness'.

Kasen and co-authors - Fritz Röpke of Max Planck Astrophysics Institute at Garching, Germany, and Stan Woosley, professor of astronomy and astrophysics at UC Stan Cruz - used supercomputers count to run some type 1a supernova simulations. The results indicate that most of the changes observed in these supernovae are due to the chaotic nature of the processes involved in the explosion.

In general, this transformation will not generate system errors when measuring if researchers use a large number of observations and apply standard corrective measures. However, the study found a small, but disturbing, impact that could make systematic differences in the chemical composition of stars at different times in the history of the universe. Researchers can use computer models to learn more about this impact and develop editing for it.

Woosley said: 'Since we have begun to understand the type-1 supernova activity, these models can be used to improve distance measurement methods, and increase the accuracy of measurements. expansion of the universe ' .

This image is based on a computer simulation of a type 1a supernova showing that the chaos and disproportionate flames of the fusion reaction occupy the entire white dwarf. (Photo: F. Ropke.)

Type 1a supernova occurs when a white dwarf has extra mass by sucking the object away from a nearby star. When it reaches a certain mass - 1.4 times the mass of the Sun is concentrated in an Earth-sized object - the heat and pressure in the center of the star produces a fusion reaction, and the white dwarf exploded. Because the initial conditions are almost identical in all cases, supernova explosions often have their brightness equivalent, and their 'light lines' (the change of light over time) are often predictable.

In essence, some supernovae are brighter, but they shine and fade more slowly, and the correlation between the brightness and the width of the light path allows astronomers to apply some corrections to pepper. standardize these observations. Astronomers can measure the light pathway of a type 1a supernova, calculate the brightness of nature, and determine their distance from us, because the brightness decreases with distance (similar to a candle looks fainter when standing far away.

Computer models used to simulate these supernovae in new research are based on the current theoretical understanding of how and where the burning process begins within a white dwarf, and at Where does it make the transition from burning slowly to exploding.

Woosley explains: 'Since combustion does not appear in the central region, and the explosion occurs first at some point near the surface of the white dwarf, the explosion is not symmetrical. This can only be studied precisely by using multidimensional calculations'.

Most previous studies used a one-way model in which simulated explosions were supposed to balance the demand. Multi-dimensional models will need more powerful computers, so Kasen's team runs most simulations on Jaguar supercomputers at Oak Ridge National Laboratory, and supercomputers at the Scientific Computer Center National Energy Research, under Lawrence Berkeley National Laboratory. The results of two-dimensional models are reported in Nature, and three-dimensional studies are still underway.

Simulations show that the asymmetry of the explosion is the key factor determining the brightness of type 1a supernovae. Kasen said: 'The reason these supernovae do not have the same brightness is closely related to breaking the symmetry'.

The main source of variation is the synthesis of new elements in the explosion. This process is very sensitive to the difference in the geometry of the first spark that stimulates the thermal response in the nucleus of a white dwarf. Nickel-56 plays a particularly important role, because the radioactive decay of this unstable isotope produces the aura that astronomers can observe for months or years after the explosion.

Kasen said: 'The decay of nickel-56 is the energy of the light. The explosion ended in just a few seconds, so what we observed was that the nickel process heated up the remnants of the explosion, and these remnants radiated light '.

In the image of a computer simulation, debris from a supernova explosion of type 1a shows unbalanced background structures formed from chaotic tongues taking over the white dwarf star. The colors represent different elements synthesized in the explosion (eg red = nickel-56). (Photo: D.Kasen et al).

Kasen developed computer code to simulate this radioactive transition, using the results of a simulated explosion to create images that can be compared directly with astronomical observations.

The good news is that the changes observed in computer models are completely consistent with Type 1a supernova observations. Woosley said: 'The most important thing, the correlation between the width and the brightness of the light line is also consistent with what observations found. So models are completely consistent with observations that detect dark energy based on '.

Another source of variation is that these asymmetric explosions look different when viewed at different angles. This leads to 20% difference in brightness, Kasen said, but the effect is completely random and produces measurements in measurements that can be reduced by observing a large number of supernovae.

The ability to lead to systematic errors first comes from the changes of the initial chemical composition of white dwarfs. The heavier elements are synthesized in supernova explosions, and remnants from these explosions are grouped into new stars. Therefore, the recently formed stars are likely to contain more heavy elements (in terms of astronomy is metallic) than the stars formed in the past.

Kasen said: 'That's what we expect to evolve over time, so if you look at the early stars in the history of the universe, they often have lower metal properties. When we calculated the effect of this factor in the models, we found that the errors in measuring the wing range would fall to less than 2%. '

Extensive research using computer simulations will allow researchers to study the impact of these changes in more detail and minimize their impact on dark energy experiments in future.